The Big Bang Theory

In the series premiere, when Leonard and Sheldon meet Penny, Leonard is immediately interested in her. But Sheldon feels his friend is chasing a dream he'll never catch.

After Leonard tries to do a favor for Penny, Sheldon ruins the plan. Leonard volunteers to sign for a package, hoping to make a good impression on Penny. However, when he involves his obsessive-compulsive roommate, Leonard sees his attempt at chivalry go horribly awry.

Leonard is depressed to learn that Penny is dating someone. As a result, encouraged by his friends and fellow scientists, Leonard actually summons the nerve to ask a woman out on a date. SARA GILBERT ("Roseanne") guest stars as Leslie.

After being fired from his job, Sheldon attempts to explore the "dreadful" life beyond physics. But his initial thrill of shopping with Penny devolves over time to him weaving ponchos as a shut-in, forcing Leonard to call on Sheldon's mother, Mary (LAURIE METCALF - "Roseanne").

After sensing that his pursuit of Penny isn't going anywhere, Leonard agrees to an unexpected sexual encounter with fellow scientist Leslie Winkle (recurring guest star SARA GILBERT). The one-night stand throws Leonard and Sheldon deep into uncharted social waters.

The socially stunted guys are nervous when Penny invites them to a party she's hosting. But they are ecstatic to find out that it's a Halloween party and enthusiastically don their respective nerdy costumes, which unfortunately fail to impress Penny's brutish ex-boyfriend. Afterwards, Koothrappali experiences the unexpected with a partygoer, Cheryl (ERIN ALLIN).

When Wolowitz seduces Penny's friend and ends up sleeping with her in Penny's apartment, Penny sleeps on Leonard and Sheldon's couch. Meanwhile, with Wolowitz occupied, the guys discover that they are without a fourth member of their group. In desperation, they ask Penny to join one of their two-person Halo teams.

Koothrappali becomes overwhelmed when his parents arrange a blind date for him, but he discovers he actually can talk to a member of the opposite sex after a few drinks. However, complications arise when his beautiful date shows more interest in Sheldon.

Sheldon and Leonard are invited to present their joint findings at a physics conference, but Sheldon refuses. Penny steps in to mediate, but this only deepens the rift between the two best friends.

After hearing Penny sing, Leonard lies to avoid seeing her perform. Sheldon goes one step further with a more elaborate lie, leading to the appearance of his nonexistent cousin. D.J. QUALLS ("Road Trip") guest stars.

When Sheldon gets sick, Leonard and the boys know what is in store for them and avoid him like the plague; this leaves an unsuspecting Penny to nurse the world's worst patient back to health.

When Leonard and Sheldon meet a 15-year-old physics prodigy, Sheldon is distraught that this boy genius is younger and smarter. In an attempt to restore a sense of purpose, the boys come up with a solution to derail the young prodigy's research.

The guys decide to compete in the university's Physics Bowl, but since Sheldon's only focus is to prove his mental superiority, the guys kick him off the team. To take his spot, they enlist his nemesis Leslie Winkle (recurring guest star SARA GILBERT).

When Leonard and the guys buy a time-machine prop from a classic 1960 movie, its arrival creates problems for Penny, and she tells the boys that their obsession with comics and toys is "pathetic."

Leonard, Wolowitz, and Koothrappali all become smitten with Sheldon's twin sister, Missy (guest star COURTNEY HENGGELER), and Leonard devises a plan to eliminate his rivals. The plan backfires, however, when Sheldon declares he will decide whom his sister dates.

When Penny learns that Leonard doesn't celebrate birthdays, she attempts to throw him a surprise party; she is sidetracked by Sheldon, however, who unexpectedly gets to live out one of his greatest fantasies at an electronics store.

When Penny breaks up with her boyfriend, Leonard finally gets up the courage to ask her out on a real date. When she says yes, each seeks the "wisdom" of a reluctant advisor -- Sheldon.

In the second season premiere, after her first date with Leonard goes awry, Penny finds an unwilling confidant in Leonard's anti-social roommate, Sheldon.

Penny and Leonard compete to see who will be the first to move on after their breakup. When Leonard sees Penny with a handsome new guy (guest star TRAVIS SCHULDT Scrubs), he enters into a rebound relationship with Sheldon's nemesis, Leslie Winkle (series regular SARA GILBERT).

Sheldon creates a monster when he introduces Penny to the world of online gaming. Especially when her addiction wreaks havoc on his life.

Rajs ego puts all of his friendships in jeopardy when he gets an inflated sense of self. Newly famous because of an article in a magazine, Raj (series regular KUNAL NAYYAR) makes a disastrous play for Leonards longtime crush, Penny.

Leonard and his friends stage an intervention to make Sheldon confront his longstanding fear of driving.

A young grad students attraction to Sheldon confuses everyone including Sheldon himself.

Sheldon and Penny engage in a battle of wills as Penny vows to get revenge on Sheldon when he bans her from the apartment for a series of petty infractions.

Wolowitz (series regular SIMON HELBERG) thinks he's found the love of his life (guest star SARA RUE) until she meets Leonard.

Sheldon can barely contain his joy when Leonard starts dating a woman (SARA RUE) who meets Sheldon's exacting standards.

Leonard just can't say no. When his relationship with new girlfriend, Stephanie starts moving too fast, Leonard turns to Penny for advice.

Leonards handsome colleague starts dating Penny. And Leonards friends are being tormented by Sheldon's obsession with gift-giving etiquette.

When Pennys comment about Wolowitzs love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting robot competition.

Socially awkward Sheldon develops a scientific procedure for making friends.

Sheldon's "simple" solution to Penny's financial problem leads to a confrontation between Leonard and Penny's hulking ex-boyfriend, Kurt (guest star BRIAN PATRICK WADE).

A disastrous visit from Mrs. Hofstadter (special guest star CHRISTINE BARANSKI) brings Leonard and Penny closer together.

A paintball game has surprising consequences for Leonard and his friends when it leads to a fight between Penny and Sheldon -- and romance for Wolowitz and Leslie.

A train trip to San Francisco takes a major detour when Leonard, Sheldon, Wolowitz and Raj discover that beautiful sci-fi actress SUMMER GLAU ("Terminator") is onboard.

Penny's home hair products business becomes a complete nightmare when a caffeine-addled Sheldon takes over.

There's a new queen bee in the building! Penny develops a rivalry with a sexy female neighbor moves in to the building and threatens to become the "new Penny."

While Stuart (guest star KEVIN SUSSMAN), a fellow comic book-loving pal of the guys, romances Penny, Leonard and Wolowitz venture out into the world of "Ladies' Night" at a local bar.

Leonard and Koothrappali take a heartbroken Wolowitz to Las Vegas, leaving Sheldon locked out of his apartment and forced to bunk with Penny.

Things begin to look up for Leonard when Penny makes a surprising revelation on her second date with Stuart (guest star KEVIN SUSSMAN). Meanwhile, Wolowitz enlists his friends' help when he discovers a critical design flaw in his project for NASA.

On the second season finale, Leonard and Penny reconsider their feelings for one another. When Leonard and his friends decide to spend the summer working -- at the North Pole -- Penny is conflicted.

On the third season premiere, Sheldon (series star JIM PARSONS) flees back to Texas in disgrace when he learns that the guys tampered with his arctic expedition data -- forcing his friends to follow him, and threatening Leonard's (series star JOHNNY GALECKI) hopes for a romantic encounter with Penny (series star KALEY CUOCO).

Leonard and Penny struggle to recover from an awkward first hookup, while Sheldon and Howard (series star SIMON HELBERG) stake their best comic books on a bet to determine the species of a cricket. LEWIS BLACK guest stars as an entymologist who settles the high-stakes bet.

Howard and Raj (series star KUNAL NAYYAR) visit a Goth nightclub to pick up women, while Sheldon attempts to build a better Penny using chocolate-based behavior modification.

Raj must find a new job or be sent back to India. Sheldon, however, has a solution -- which leaves Leonard and Penny dealing with Howard as third wheel.

While Sheldon settles a score with his nemesis, Star Trek: The Next Generation's WIL WHEATON (guest starring as himself), Wolowitz begs Leonard to get Penny to set him up with one of her friends.

Sheldon teaches Leonard how to understand football, while a kite-fighting incident threatens Howard and Raj's friendship.

Sheldon plays the peacemaker when an argument between Leonard and Penny proves "inconvenient" to him.

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke (guest star JOHN ROSS BOWIE), and the guys help Sheldon exact his revenge. Meanwhile, Wolowitz tries not to destroy his new relationship with Bernadette (guest star MELISSA RAUCH). KATEE SACKHOFF (Battlestar Galactica) makes a cameo as Wolowitz's dream girl.

Sheldon takes on his greatest challenge when he attempts to help Penny understand physics, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

A visit from Leonard's mother (guest star CHRISTINE BARANSKI) delights Sheldon and horrifies Leonard.

While Sheldon and Koothrappali attend a university mixer, Leonard is upset to discover that Penny believes in psychics. DANICA McKELLAR (The Wonder Years) guest stars as the object of Raj's attraction.

When their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system -- and Sheldon struggles to cope.

Suffering from a case of "physicist's block," Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

It's Valentine's Day, and Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland. Will it be Sheldon or Penny?

Sheldon misses his chance to meet comic book legend STAN LEE (as himself) when he winds up in traffic court after he gets a ticket because of Penny.

When the guys find a rare movie prop ring from The Lord of the Rings at a garage sale, it threatens to tear them apart -- forcing them to choose the ring or their friendship.

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

A fight between Leonard and Penny threatens their relationship, while Sheldon battles WIL WHEATON (guest starring as Himself) in bowling.

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy and gets caught in a lie.

Leonard and Sheldon compete for the attention of a famous female physicist -- Dr. Elizabeth Plimpton (guest star JUDY GREER).

Leonard tells Penny the story of how he met Sheldon for the first time...and what happened to the elevator.

In the third season finale, Wolowitz and Koothrappali search for Sheldon's perfect match online -- and find Sheldon's ideal woman (guest star MAYIM BIALIK). Meanwhile, Penny worries that dating Leonard has ruined her for normal guys.

On the fourth season premiere, Penny (series star KALEY CUOCO) finds herself along for the ride on Sheldon's (series star JIM PARSONS) first date ever. Meanwhile, Wolowitz (series star SIMON HELBERG) finds a new use for a robotic arm. MAYIM BIALIK guest stars as Sheldon's date, Amy Fowler.

When Sheldon realizes he won't live long enough to download his consciousness into a robot body, he attempts to extend his lifespan. Apple Co-Founder STEVE WOZNIAK guest stars as Himself.

The guys are concerned as Sheldon searches for an alternative to human companionship after he and Amy (MAYIM BIALIK) break up. LAURIE METCALF reprises her role as Sheldon's mother.

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work. Battlestar Galactica's KATEE SACKHOFF and Star Trek's GEORGE TAKEI guest star as themselves as Wolowitz's love gurus. MELISSA RAUCH reprises her role as Howard's girlfriend, Bernadette.

Leonard realizes he's the only one without a girlfriend, while Sheldon wants to get rid of his.

A visit from Raj's sister (guest star AARTI MANKAD) creates tension among the guys -- especially when Leonard keeps an affair secret from Sheldon, Howard and Raj.

When an FBI agent (guest star ELIZA DUSHKU) interviews the guys for Wolowitz's security clearance, Sheldon's answers during the screening, put Wolowitz's clearance in jeopardy.

When the guys camp in line for a screening, their plans are thwarted by Sheldon's greatest nemesis, WIL WHEATON (guest starring as himself). Meanwhile, Penny and Bernadette invite Amy to her first slumber party.

Penny asks Leonard to lie to her father, Wyatt (guest star KEITH CARRADINE), while Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy finds she has sexual feelings for Penny's ex, Zack (guest star BRIAN THOMAS SMITH) while Koothrappali and Wolowitz try to prove who would be the better superhero.

The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.

Leonard's idea for a smartphone app derails his friendship with Sheldon as they fight for control of the project.

Tension runs high when everyone is staying at the same hotel for a science event and Bernadette runs into her ex-boyfriend (guest star RICK FOX, three-time NBA champion with the Los Angeles Lakers).

Sheldon wants Penny to give him acting lessons, hoping that they will help him become a better teacher. Meanwhile, Koothrappali fantasizes about his best friend's girlfriend.

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science. JESSICA WALTER (Arrested Development) guest stars as the widowed benefactress and JOSHUA MALINA (The West Wing) guest stars as the University President.

As Wolowitz contemplates taking things with Bernadette to the next level, he must choose between his girlfriend and his mother. Meanwhile, Leonard rekindles his relationship with Raj's sister, Priya.

When the gang starts hanging out at Raj's and Sheldon realizes it's actually Leonard who is the center of their social group, Sheldon decides to get a new group of friends.

Leonard must choose between his new girlfriend, Priya, and his friendship with Penny. Meanwhile, Howard drives Sheldon crazy with a magic trick.

When someone hacks Sheldon's online gaming account, the guys go on a quest to find the culprit.

Sheldon and Amy experiment on their friends by spreading gossip, while Howard takes a big step in his relationship with Bernadette.

Priya uses her lawyer skills to pick apart the roommate agreement...and put Sheldon in his place. Meanwhile, the girls take Sheldon dancing.

Raj attempts to cure his social anxiety disorder of talking to women, while Penny uses Bernadette to spy on Leonard and his girlfriend.

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.

When Bernadette receives her Ph.D., the guys take joy in reminding an emasculated Wolowitz that he is the only one in their group who isn't a doctor. Meanwhile, Koothrappali becomes Sheldon's new roommate after hearing Leonard and Priya engaging in a Star Trek bedroom fantasy, on the fourth season finale.

The fifth season premiere picks up where the fourth season finale left off as the gang deals with the aftermath of Penny and Raj's night together. While Penny worries that she's screwed things up permanently with her friends, Sheldon takes command of the paintball team. Emmy® nominee CHRISTINE BARANSKI (The Good Wife) reprises her role as Leonard's emotionally distant mother.

A battle of wills between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya (recurring guest star AARTI MANN), who has moved back to India.

Leonard attends a co-worker's wedding as Amy's date. Meanwhile, Howard tries to convince Bernadette to live with his mom after they get married by suggesting a trial run with the two of them staying with his mom over the weekend.

When Raj is upset he's the only one of the four guys who is not in a relationship, Penny sets out to find the perfect date, introducing him to Emily (guest star KATIE LeCLERC -- Switched at Birth) a girl he can actually talk to!

Sheldon's old nemesis, WIL WHEATON (guest starring as Himself), returns and invites everyone to a housewarming party. Sheldon threatens to "defriend" Leonard if he attends. But when he hears that BRENT SPINER (guest starring as Himself), the actor who played Commander Data, will be there, Sheldon decides to go to the party after all... only to discover new levels of treachery. Meanwhile, Howard gets an out-of-this-world opportunity that Bernadette reacts to strongly.

Craving a little motherly love, Sheldon competes with the gang for his mother's attention when she comes to visit. LAURIE METCALF reprises her role as Sheldon's mother, Mary.

A cute comic book artist (guest star COURTNEY FORD) puts Leonard's relationship with Priya to the test; while Sheldon, getting into the spirit of Halloween, tries to scare the guys.

Amy is heartbroken when Bernadette and Penny go shopping for wedding dresses without her.

Can friends with benefits still be friends without? Leonard and Penny try hanging out alone, while Sheldon must overcome his fear of birds.

Sheldon becomes jealous and considers taking his relationship with Amy to the next level when Stuart (guest star KEVIN SUSSMAN) from the comic book store asks her out on a date.

Leonard must face his fears after being contacted by his high school tormentor (guest star LANCE BARBER), while Penny realizes that she might have been a bully herself.

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and it's up to Penny to teach him how to be a better boyfriend. Howard, meanwhile, must come to grips with Bernadette's dislike of children.

The possibility of Leonard and Penny getting back together could prove disastrous when Leonard offers Penny a spur of the moment invitation to a romantic dinner for two on the 100th episode of the series.

Leonard and Penny experiment with dating again by "beta testing" their relationship, while Raj develops a peculiar relationship with his phone's virtual assistant.

Sheldon's selfish demands force Leonard to reconsider their friendship. Could this be the end of The Roommate Agreement? Meanwhile, Howard tries to pick his astronaut nickname, but NASA astronaut MIKE MASSIMINO (guest starring as himself) has other ideas.

When Sheldon is forced to take a vacation by the university, he goes to work with Amy in her neurobiology lab. Meanwhile, Bernadette wants Howard to sign a pre-nuptial agreement.

When a corner office at the University opens up, Sheldon must compete for it with his office nemesis, Barry Kripke. Meanwhile, a personal gift from Amy makes Penny uncomfortable.

Sheldon's life is turned upside-down after his barber becomes hospitalized. Now, that there's been a change in his routine, Sheldon finds himself re-evaluating his entire life. Meanwhile, astronaut training causes Howard to rethink his decision to go into space.

It's on...like Alderaan, when the guys plan a weekend Star Wars gaming marathon! But when Sheldon chooses the guys-only weekend over a weekend with Amy to visit her aunt, he is destined to feel the force!

It's a dream come true for Sheldon when he has a close encounter with his hero, Mr. Spock. Legendary sci-fi icon LEONARD NIMOY guest stars, lending his voice to a unique reprisal of his three-time Emmy®-nominated Star Trek role.

When Wolowitz gets tow work with world-renowned scientist STEPHEN HAWKING (guest starring as Himself), Sheldon is willing to do anything to meet his hero.

Howard's wedding plans are in jeopardy after the guys (and Wil Wheaton) throw him a bachelor party. After details of his sexual history are leaked online, Bernadette reconsiders marrying Howard.

When NASA reschedules Howard's mission and puts his wedding plans in jeopardy, he's forced to face his fears and Bernadette's dad (guest star CASEY SANDER). Meanwhile, Leonard says something surprising to Penny in the bedroom.

Howard Wolowitz crosses over into the final frontiers of space...and marriage on the fifth season finale. When Howard and Bernadette decide they want to be married before his NASA space launch, the gang rushes to put on a wedding. NASA Astronaut Mike Massimino guest stars as Himself.

On the sixth season premiere, Howard discovers that he can't escape his mother -- even in space! Caught in an argument between Bernadette and his mom (recurring guest voice CAROL ANN SUSI), Howard deals with woman trouble from the International Space Station. Back on earth, meanwhile, Raj faces his loneliness, by turning his existence as a third wheel into an art form.

When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. But Sheldon is no good at keeping secrets. Meanwhile, Howard is being picked on in space by the other astronauts (guest stars PASHA LYCHNIKOFF and MIKE MASSIMINO).

While the pressures of being in space starts to take its toll on Howard, Amy feels threatened when Sheldon hires a young female assistant, Alex (guest star MARGO HARSHMAN).

When Howard returns from space, he doesn't get the hero's welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.

The gang celebrates Halloween at Stuart's comic book store. Meanwhile Leonard and Penny discover a new spark in their relationship when he seduces her with science. And while Howard can't stop talking about space, it takes iconic astronaut BUZZ ALDRIN (guest starring as himself) to get him grounded again.

Sheldon's tenuous relationship with renowned scientist STEPHEN HAWKING is threatened by a game of "Words with Friends," while Penny secretly enrolls in a class at the local college.

Pressured by Bernadette, Howard comes to terms with moving out of his mother's house. Meanwhile, Sheldon, who's caught in the middle of a feud between his "girlfriend" Amy and good friend WIL WHEATON, goes to Penny for advice. Star Trek's LeVAR BURTON guest stars.

Howard and Raj try to get to the bottom of why Sheldon disappears every afternoon at 2:45. Meanwhile, Leonard and Penny wrestle with jealousy in their relationship.

When the University reassigns Sheldon's (unused) parking spot to Howard, the ensuing turf battle affects the whole gang.

Sheldon plays nursemaid to a sick Amy, while Howard attempts to bond with his father-in-law (guest star CASEY SANDER) on an upcoming fishing trip.

Sheldon unwillingly revisits some Christmas memories during a lively game of Dungeons and Dragons, while Penny, Bernadette and Amy try to find the perfect girl for Raj when he joins the girls for ladies night.

Sheldon is accused of sexual harassment at the Univesity and winds up dragging Leonard, Raj and Howard into the fray. Southland's REGINA KING guest stars as the University's Director of Employee Relations.

While the guys take a road trip to a comic book convention in Bakersfield dressed as characters from Star Trek: The Next Generation, Leonard's car is stolen. Meanwhile, the girls stay home and try to appreciate the world of comics.

Outraged that he's being forced to work with his university nemesis, Barry Kripke (guest star JOHN ROSS BOWIE), Sheldon faces a crisis of conscience. Meanwhile, Howard and Raj spend a thousand dollars on action figures of themselves.

A fight between Leonard and Sheldon drives Leonard to finally move in with Penny -- not realizing how the shift will affect Penny and Amy's living arrangements. Meanwhile, Raj takes care of Mrs. Wolowitz while Howard is away.

While the guys try to give their significant others the perfect Valentine's Day, Raj and Stuart throw a lonely people party at the comic book store.

After a terrible date, Raj vows to never leave his apartment again. Meanwhile, Penny actually impresses Sheldon with her acting skills.

Back to school! Leonard, Sheldon and Howard try to advance the cause of women in science by speaking with junior high girls about their future careers, while Raj plans his date with Lucy (guest star KATE MICUCCI).

When Howard finds a letter from his father, he's forced to confront his past, struggling with whether or not he should open it. And Leonard and Penny throw a "grown-up" cocktail party at the apartment.

Let the battle begin! Leonard, Sheldon and Raj fight for tenure at the University -- and the competition heats up when the girls get involved!

Sheldon feels lost after one of his favorite TV shows gets canceled too soon, so Amy tries to help him get over his compulsive need for closure. Meanwhile, Raj discovers a secret about his new love interest, Lucy.

Sheldon and Leonard hire Professor Proton (guest star BOB NEWHART), the host of their favorite childhood TV show, to perform. Also, Howard and Bernadette run into trouble babysitting Raj's dog.

When the girls' trip to Vegas falls through, the guys invite them to play Dungeons & Dragons -- causing Sheldon and Amy's relationship to take an unexpected turn. Meanwhile, Raj and Lucy go on a very awkward date.

When Leonard is offered an exciting new job opportunity overseas, Sheldon grows very jealous and Penny is thrown for a loop. Meanwhile, Raj pushes Lucy a little too far in their relationship on the sixth season finale.

On the one-hour seventh season premiere, Sheldon and Penny bond in Leonard's absence, but it's Sheldon's feelings that are crushed when Leonard returns from the North Sea. Guest star REGINA KING returns as Mrs. Davis, the University's Director of Employee Relations.

On the second part of the one-hour seventh season premiere, Raj gets consoled about his ex-girlfriend and Howard's relationship with his mother causes an unusual threat to his masculinity. KEVIN SUSSMAN returns as Stuart, the comic book store owner.

When the entire gang competes in a cutthroat scavenger hunt designed by Raj that tests their science knowledge and street smarts, it brings out the best -- and worst -- in everyone.

After Amy ruins one of Sheldon's favorite movies -- Raiders of the Lost Ark -- he gets defensive, seeking revenge. Meanwhile, Leonard discovers a way to get Penny to do anything; and Raj and Stuart create online dating profiles.

Sheldon must decide how much "Amy time" is too much after she takes a job at his university, and their relationship is put to the test. Meanwhile, Howard finds himself sleeping on Raj's couch after a fight with Bernadette.

Sheldon's latest scientific breakthrough makes him feel like a fraud -- and threatens to haunt him forever. Meanwhile, Howard's romantic gesture to Bernadette causes Penny to step up her game with Leonard.

Sheldon feels slighted when Professor Proton (recurring guest star BOB NEWHART) seeks advice from Leonard instead of him, and he seeks revenge by befriending a rival science TV host, BILL NYE (guest starring as Himself). Meanwhile, Raj gets jealous when Howard crashes "girls' night."

Leonard tries to keep Sheldon from overreacting when a past mistake comes to light, but Sheldon punishes Leonard by making him "walk a mile in his shoes." Meanwhile, Penny confronts Raj's ex-girlfriend, Lucy (guest star KATE MICUCCI).

An upset Sheldon protests when the entire gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

Leonard and Amy help Sheldon cope with the shame he's feeling after his accidental contribution to science is disproved. Meanwhile, Raj must stay with Howard and Bernadette for a week. IRA FLATOW guest stars as Himself.

While Sheldon is away in Texas, everyone gathers to decorate the apartment Christmas tree, and imagines what their lives would be like if they had never met Sheldon.

When Penny's big acting break on NCIS is a bust, Leonard struggles to help her, which results in Penny asking Leonard a bold relationship question. Meanwhile, Sheldon tries to learn how to be funny and Raj tries to work on his "game" before talking to girls.

When Sheldon is forced to take a vacation, he tries to relax, but instead spends a lot of time with Penny after she quits her job. Meanwhile, Leonard struggles to be supportive of Penny and Bernadette seeks Stuart's help in replacing one of Howard's comic books.

After they guys can't get Comic-Con tickets, Sheldon decides to hold his own convention, and winds up spending a wild night with JAMES EARL JONES (guest starring as himself). Meanwhile, the girls see if they can act like "grown-ups." Star Wars icon CARRIE FISHER makes a cameo appearance as well.

Love is in the air when Amy convinces Sheldon to join her (as well as Howard and Bernadette) for a romantic weekend in Napa Valley to celebrate Valentine's Day. Meanwhile, Leonard and Penny must rush Raj's dog to the vet.

When Leonard buys a dining room table, it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back to space and Bernadette struggles with whether or not to encourage him.

Howard invites Sheldon to travel to Houston with him in an attempt to improve their friendship, while Penny's offered an embarrassing role and Raj asks Amy for help with a girl.

When Sheldon visits his mom (recurring guest star LAURIE METCALF) in Houston, he is forced to confront a new reality. Meanwhile, Raj's "Murder Mystery" party starts some fights within the gang.

While Raj is wracked with guilt over dating two women at the same time and Penny is wrestling with whether to take a role in a cheesy movie, Amy must help Sheldon through the even greater hell of choosing between two gaming systems.

Sheldon faces a personal crisis after deciding he's wasting his time with String Theory. Meanwhile, a double date between Raj, Emily and the Wolowitzes ends in embarrassment for Howard.

Leonard tries to help Sheldon free his mind by reinstating "Anything Can Happen Thursday," but when Sheldon tries to be spontaneous, it leads to unexpected friction between Penny, Amy and Bernadette. Meanwhile, Raj seeks Howard's help in preparing for a date with Emily.

May the "Fourth" Be With You! Professor Proton helps Sheldon cope with grief, while Leonard turns a relationship milestone into a competition with Penny. Meanwhile Amy and Bernadette make a "Star Wars Day gift for the guys.

A horrible day at work prompts Penny to evaluate her life choices -- including taking a big step with Leonard. Meanwhile, Howard and Bernadette struggle to care for Mrs. Wolowitz, and Raj gets relationship advice from Sheldon.

With his entire world changing around him, Sheldon is forced to confront an uncertain future and considers a major move in the seventh season finale. Meanwhile, Raj and Emily take it to the next level, and Mrs. Wolowitz's injury is a major headache for Howard and Bernadette. Recurring guest star CHRISTINE BARANSKI returns as Leonard's mother, Beverly Hofstadter.

Leonard and Sheldon (series stars JOHNNY GALECKI and JIM PARSONS) are brilliant physicists – geniuses in the laboratory, but socially challenged everywhere else. Enter beautiful, street-smart neighbor, Penny (series star KALEY CUOCO-SWEETING), who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten engaged. Even Sheldon has found a female companion – entering into a “Relationship Agreement” with neurobiologist Amy Farrah Fowler (series star MAYIM BIALIK). In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Raj (series star KUNAL NAYYAR) and Howard (series star SIMON HELBERG), and Howard's adorable microbiologist wife, Bernadette (series star MELISSA RAUCH).

When Sheldon is forced to teach a class, Howard surprises everyone by taking it. Meanwhile, the tension between Penny and Bernadette gives Amy a chance to play both sides. Guest star REGINA KING returns as Mrs. Davis, the University’s Director of Employee Relations.

Howard is nervous when NASA asks him to throw out the first pitch at a Los Angeles Angels game for National Space Day. Also, Leonard and Penny try to prove Sheldon wrong after he claims that he and Amy are a superior couple.

Raj’s honesty about his past comes back to bite him after his girlfriend, is cold to Penny. Meanwhile, the guys consider becoming part-owners in Stuart’s comic-book store.

Amy and Bernadette accuse Penny of being a “buzzkill” after she gets an email from work during their Vegas weekend. Meanwhile, the guys try to invent something cool, but only come up with new ways to procrastinate.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Meanwhile, Leonard and Penny seek advice from Wolowitz and Bernadette after they fight about money.

The guys try to help Penny out of an awkward work dilemma, when a smitten doctor shows up at her door after her flirtatious sales techniques work a little too well. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

When the gang recreates a high-school prom night on the roof of the guys’ apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj’s parents’ impending divorce causes Howard and Bernadette to work on their own marriage.

While Sheldon says a tearful goodbye to the final installment of “Fun with Flags,” Leonard, Howard and Raj search for something significant in a dead professor’s research. And Bernadette is shocked to learn of her co-workers’ true feelings from Penny.

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays

When the guys finally agree to do something the girls like, it leads to a confrontation between Leonard and Sheldon.

Sheldon worries his comfortable lifestyle is preventing him from achieving scientific progress so he asks his friends to make him miserable.

After Leonard and Sheldon co-publish a physics paper, they must defend themselves against criticism from an online bully. Also, girls’ night finds Penny, Amy and Bernadette confronting embarrassing moments from their pasts.

Howard receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store. Penny teaches Sheldon how to “let it go” but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.

When the gang hears about an experiment designed to make participants fall in love, Sheldon and Penny put it to the test as a joke. Meanwhile, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a “zombie.” And Bernadette and Howard run into trouble at the airport after returning from the funeral for Mrs. Wolowitz.

A trip to the pet store ends in a fight when Amy learns that Sheldon has applied for a one-way mission to colonize Mars. Also, Leonard surprises Penny with a very “adult” purchase; and Raj is caught snooping in Emily’s apartment.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. And a blackout at Mrs. Wolowitz’s home leads to a final family dinner in her honor.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to sneak on to George Lucas’s Skywalker Ranch to meet one of their idols. Back in Pasadena, Howard and Bernadette battle over the fate of his Dr. Who TARDIS, while Raj and Amy offer to settle the dispute with a game of ping pong.

When Sheldon and Amy build a blanket fort, they come to a big crossroads in their relationship. And Wolowitz is shocked when a man claiming to be his half-brother he never knew he had shows up at his front door. And, when Penny is invited to appear on Wil Wheaton’s podcast, she and Leonard have a huge, on-air argument.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Meanwhile, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

Wolowitz questions his engineering abilities when he and Sheldon can’t get a drone to fly. Meanwhile, a canceled flight nearly prevents Leonard from giving the commencement address at his former high school. And Raj pits his parents against each other when his father cuts him off financially.

Personalities collide and sparks fly when Sheldon and Leonard’s mothers (special guest stars LAURIE METCALF and CHRISTINE BARANSKI) finally meet. Meanwhile, Howard decides to “man up” and do his fair share of the housework – but not without a little help from his friends.

In the eighth season finale, Sheldon presses Leonard and Penny to choose a date for their wedding, while dealing with dramatic changes in his own relationship with Amy.

In the ninth season premiere, Penny struggles with Leonard’s confession that he kissed another girl while on the North Sea. After driving to Vegas, Penny must now decide whether she wants to go through with the wedding. Back home, Sheldon doesn’t know how to act after Amy pushes pause on their relationship.

After Amy breaks up with Sheldon, he tries to retaliate by filming a special episode of “Fun with Flags.” Leonard, meanwhile, confronts the woman he kissed on the North Sea in an attempt to put Penny’s mind at ease, and Bernadette feels guilty about withholding a secret from Penny.

The guys’ science skills are put to the test when they get a flat tire during Leonard’s surprise bachelor party weekend in Mexico. Meanwhile, the girls force Penny to finally tell her family that she eloped with Leonard.

When Penny and Leonard announce they’re moving in together, Sheldon decides to revert back to 2003 – a simpler time before he met either of them. Meanwhile, Howard and Raj form a band to play at the Comic Book Store.

When the guys take fencing lessons from Barry Kripke (recurring guest star JOHN ROSS BOWIE), Sheldon finds himself in an awkward position when Kripke expresses interest in Amy. Also, Stuart struggles to bring in female customers into the Comic Book Store, so Penny, Amy and Bernadette come by to help him out.

In the midst of a nationwide helium shortage, Sheldon and Leonard take desperate measures to obtain the supplies they need on the black market. Meanwhile, Penny and Bernadette download a dating app on Amy’s phone in order to find her a new man. MICHAEL RAPAPORT guest stars as their Black Market dealer, Kenny.

While being interviewed for a documentary about Spock, Sheldon struggles to suppress his emotions about his recent break-up with Amy – leaving Leonard and Penny shocked to discover that Sheldon had an engagement ring for Amy. Meanwhile, Howard and Bernadette disagree over remodeling his childhood home. WIL WHEATON, ADAM NIMOY and STEPHEN MERCHANT guest star.

With Amy out on a date with a mystery man, Sheldon enlists the help of Howard and Raj to find a new girlfriend by posting online. And when Amy is coy with the details about the guy she’s dating, Penny and Bernadette decide to spy.

Sheldon and Amy try hanging out as friends when they spend Thanksgiving together at the Aquarium. Meanwhile, Howard reluctantly agrees to volunteer at the soup kitchen with Bernadette, Raj and Emily, while Penny discovers that Leonard knows more about her than she thought.

After driving Leonard and Penny crazy by his desperate attempts to remember the name of a song stuck in his head, Sheldon has a revelation when he realizes why. Then, despite their previously awkward date, Amy invites Dave (recurring guest star STEPHEN MERCHANT) over for dinner. And Howard and Raj become obsessed with a fan of their band, Footprints on the Moon.

After more than five years of dating, Sheldon and Amy spend their first night together; while Leonard, Howard and Raj must decide who will take their extra Star Wars movie ticket. Recurring guest star BOB NEWHART returns as Sheldon’s Obi-Wan to advise him on his difficult relationship decisions.

Penny gets more than she bargained for when Leonard agrees to meet with a psychiatrist on her behalf. Sheldon and Raj collaborate on an astronomical discovery. Howard and Bernadette can’t believe what they’re feeling after Stuart moves out.

After having to deal with Sheldon being sick, Leonard, Penny and the gang try to treat themselves to a Sheldon free weekend.

Sheldon’s thrilled when his Meemaw (guest star JUNE SQUIBB) comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl (guest star ALESSANDRA TORRESANI) at the comic book store who makes him question his relationship with Emily.

Sheldon and Amy host a special live Valentine's Day episode of "Fun with Flags." While Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub; and Raj is torn between Emily and the cute girl he met at the Comic Book Store.

When the gang finds out about Bernadette’s pregnancy, they celebrate by singing karaoke. Meanwhile, Bernadette is concerned when Howard freaks out over her pregnancy announcement, as he’s convinced that he needs to make more money to provide for the baby.

After more than nine years together, the gang finally celebrates Sheldon’s birthday with a few special guests on the 200th episode. CHRISTINE BARANSKI, SARA GILBERT and WIL WHEATON return and are joined by special guest star ADAM WEST.

Leonard, Sheldon and Howard run into problems when they file for a patent for their infinite persistence gyroscope. Meanwhile, Penny, Amy and Bernadette give Raj dating advice after Emily reaches out to him after their breakup.

When Sheldon’s laptop dies, it leads him to share a deep secret with Amy after she buys him a new one; Meanwhile, Raj sells out Leonard and Howard after they lie to their wives in order to attend an early screening of a movie.

Sheldon spills a secret of Leonard’s when the two take a weekend cabin trip with Penny and Amy; Meanwhile Howard and Bernadeitte must draw the line when Raj goes overboard with pregnancy gifts.

When a small argument between Leonard and Sheldon erupts into a heated fight, everyone must take sides during a group get-together.

The gang goes to a wine bar and runs into Penny’s old boyfriend, Zack (recurring guest star BRIAN THOMAS SMITH); Bernadette gets stuck spending the evening with Sheldon when she can’t go wine tasting with the group, and things don’t go as planned when Raj introduces his new girlfriend, Claire (ALESSANDRA TORRESANI).

Sheldon hires Stuart to spend the day with Amy when he’d rather go to a movie screening. Also, Leonard’s mother, Beverly, comes to town and Penny struggles to make a connection with her.

Chaos ensues in the ninth season finale when Leonard’s recently divorced parents (special guest stars JUDD HIRSCH and CHRISTINE BARANSKI) and Sheldon’s devoutly religious mother come to town. Meanwhile, Howard and Raj think the government is out to get them, when they’re contacted about their guidance system.

In the tenth season premiere, Penny’s family arrives for the wedding ceremony, including her anxiety-ridden mother, Susan (guest star KATEY SAGAL), her drug-dealing brother, Randall (guest star JACK McBRAYER) and her father Wyatt (returning guest star KEITH CARRADINE). After Sheldon’s mother, Mary (recurring guest star LAURIE METCALF) and Leonard’s father, Alfred (returning guest star JUDD HIRSCH) share an evening together, however, everyone deals with an awkward morning the next day. Recurring guest star CHRISTINE BARANSKI returns as Leonard’s mother, Dr. Beverly Hofstadter, while Breaking Bad’s DEAN NORRIS guest stars as Air Force Representative Colonel Williams.

Colonel Williams, an Air Force representative from the Department of Material Command, sits down for a talk with Howard.

Tensions rise when the guys struggle to complete their government project on time – and Sheldon tries an energy drink to stay awake. Also, Penny and Amy go to a “party” at the house of Bert, the geologist (guest star BRIAN POSEHN). And Raj learns Bernadette’s true feelings about her pregnancy when they clean out the future baby room. Dean Norris returns as Air Force Colonel Williams.

When Amy’s apartment floods, she proposes a “cohabitation experiment” with Sheldon. Meanwhile, Howard and Bernadette are upset when Raj learns the gender of their baby before they do.

Leonard and Penny must separate a quarreling Sheldon and Amy, when their cohabitation experiment doesn’t go as planned. Sheldon threatens to break off their relationship when Amy refuses to adhere to the “bathroom schedule.” Also, Howard and Bernadette find unexpected guests at their house when they decide to stay home from a planned vacation.

Penny is surprised to learn she has fans of her performance in “Serial Ape-ist” when she attends the Van Nuys Comic-Con with Leonard. Also, Amy hosts a Sheldon-style brunch at Penny’s apartment. And Howard makes an impulsive purchase when he starts stressing out about the baby on the way.

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment; and they host an “on location” episode of “Fun with Flags” in Penny’s apartment. Also, Leonard lets Penny decorate Sheldon’s old room after she learns that she has secretly been moving Leonard’s collectibles into storage.

After a successful experiment combining their genes, Sheldon will stop at nothing to convince Amy they should procreate. Also, Raj is embarrassed to tell the gang what the new woman he’s dating does for a living.

When CalTech geologist Bert (recurring guest star BRIAN POSEHN) wins the MacArthur Genius Fellowship, Sheldon is overcome with jealousy. Meanwhile, Howard finds an old remote control Stephen Hawking action figure he invented. STEPHEN HAWKING returns to guest star as himself.

A battle ensues when Leonard and Sheldon argue over who will get custody of their shared belongings. Also, Raj and Stuart fight to be the most helpful during Bernadette’s final weeks of pregnancy. CHRISTOPHER LLOYD guest stars as Theodore.

While Sheldon and Amy celebrate Amy’s birthday, Howard and Bernadette welcome their new Baby Wolowitz.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas. Laurie Metcalf returns as Sheldon’s mother, Mary.

After Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy, leaving Sheldon to play the unlikely peacemaker. Meanwhile, Howard and Raj try to fix a squeaky floorboard in the baby’s room.

Sheldon beta tests an MIT invention that helps him read people’s emotions. Meanwhile, Raj invites his ex-girlfriends over to give him dating advice, and Leonard can’t hide his feelings when Penny announces that her brother is coming to town. Guest stars LAURA SPENCER, KATE MICUCCI, ALESSANDRA TORRESANI and KATIE LeCLERC return as Raj’s ex-girlfriends.

Leonard and Howard try to distract Sheldon with tickets to a historic railway when he slows the progress of their guidance system. Meanwhile, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley. Dean Norris returns as Colonel Williams.

Sheldon and Amy have their first fight since moving in together, after he shares intimate details of their relationship with people at the university. Meanwhile, Raj is shocked by the realities of financial independence when he stops receiving support from his father (guest star BRIAN GEORGE).

When Raj is cut off from his father’s fortune, he appoints Sheldon in charge of his finances to help him get out of debt. Also, Penny considers joining Leonard at Comic-Con.

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon’s old room. Christine Baranski returns as Leonard’s mother, Beverly.

Leonard, Penny and Raj adjust to their new living arrangement, while Sheldon takes an interest in Amy’s work.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Howard as well as Amy on the same day. Also, Bernadette nears the end of her maternity leave and must return to work. JOEL MURRAY guest stars as Doug.

Howard and Bernadette have a hard time leaving Halley in daycare when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca (guest star APRIL BOWLBY).

Leonard isn’t thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack (guest star BRIAN THOMAS SMITH).

After Leonard, Sheldon and Howard celebrate the completion of their top secret Air Force project, they’re met with an unpleasant surprise. Also, Amy is offered a summer position as a visiting researcher.

On the tenth season finale, the gang is concerned when Sheldon’s former admirer, Dr. Ramona Nowitzki (returning guest star RIKI LINDHOME) resurfaces while Amy is away at Princeton.

Highlights of the Q&A with the cast and creators

Cast members discuss the best romantic moments from Season 6.

Join The Big Bang Theory's executive producers and writers at the Comic Con 2013 Panel, discussing the creative process for the first time.

What happens when Kaley, Mayim, and Melissa encounter a precocious threesome who bear a striking resemblance to their younger selves? Cute overload!

Comedy folk duo Garfunkel and Oats (Kate Micucci and Riki Lindhome) lend their unique brand of songwriting to help Wolowitz serenade his quarantined bride Bernadette.

In honor of Star Wars Day, BBT enlists the help of legendary FX studio, Industrial Light and Magic to imbue Professor Proton (Bob Newhart) with the powers of a Jedi master.

When silver screen titan James Earl Jones makes a guest appearance on BBT, everyone knew it was going to be a blast, but no one suspected the man behind Darth Vader's voice would be laughing hardest!

Outtake footage of the Cast and Crew.

Series director Mark Cendrowsi takes the audience on a guided tour of the non-stop action he and the cast endure every week while filming The Big Bang Theory.

The Executive Producers, Writers and Cast reveal what's coming in Season 8.

A tribute in memory of the late Carol Ann Susi.

Gag Reel

Behind the scenes of Billy Bob Thornton’s
guest starring role.

A documentary about the search for the world's biggest BBT Superfans and their trip to LA to meet the cast and crew on set.

The cast of The Big Bang Theory answers fan questions from Twitter.

Comic-Con Writer's Panel

The cast of The Big Bang Theory answers fan questions from Twitter

The stars and creative team of The Big Bang Theory celebrate a milestone, their 200th episode, featuring their best moments, behind the scenes footage of episode 200 and red carpet interviews from the event.

The stars and creative team of The Big Bang Theory celebrate the recipients of the new "Big Bang Theory Scholarship" which awards students pursuing degrees in STEM fields, featuring behind the scenes footage of the scholarship reception on set.

The cast of The Big Bang Theory answers fan questions from Twitter.

Writer's Panel at the 2016 San Diego Comic-Con.