Self-organization, that is to say, the phenomena by which a system self-organizes its internal structure independent of external causes, is a fundamental property of open and complex systems. Such systems also exhibit phenomena of nonlinearity, instability, fractal structures and chaos - phenomena which are intimately related to the general sensation of life and urbanism at the end of the 20th century. On the other hand, self-organization is a formal theory. It is, in fact, a general umbrella for several theoretical approaches which, while they agree on general principles, differ in their treatment of such systems, in the emphasis they give to the various processes and properties and in the subject matter they refer to. In this paper I discuss some of those theories and methodologies of self-organization which were applied to the domain of cities and urbanism. The discussion proceeds under the title of seven categories of cities which are related to general theories or specific methodologies: dissipative cities, synergetic cities, chaotic cities, fractal cities, cellular automata cities, sandpile cities, and FACS and IRN cities. The discussion of each category of cities starts with a short introduction to the general principles of the approach and then elaborates on its self-organizing city.