This book describes in detail the scientific philosophy of the formation and stabilization-destabilization of foams. It presents all hierarchical steps of a foam, starting from the properties of adsorption layers formed by foaming agents, discussing the properties of foam films as the building blocks of a foam, and then describing details of real foams, including many fields of application. The information presented in the book is useful to people working on the formulation of foams or attempting to avoid or destruct foams in unwanted situations.