Two digital revolutions--computing and communication--have radically transformed our economy and lives. A third digital revolution is here: fabrication. Today's 3D printers are only the start of a trend, accelerating exponentially, to turn data into objects: Neil Gershenfeld and his collaborators ultimately aim to create a universal replicator straight out of Star Trek. While digital fabrication promises us self-sufficient cities and the ability to make (almost) anything, it could also lead to massive inequality. The first two digital revolutions caught most of the world flat-footed, thanks to Designing Reality that won't be true this time.