To understand the changing structures of American cities, it is important to setout the assumptions and theories that guide this study. We follow the Kurt Lewin ( 1936) dieturn that, "from a practical point of view the mere gathering of facts has very limited value. It cannot give an answer to the question that is most important for practical purposes-namely, what must one do to obtain a desired effect in given concrete cases? To answer this question it is necessary to have a theory, but a theory which is empirical and not speculative. This means that theory and facts must be closely related to each other." As we teil our graduate students preparing for careers in local government leadership, there is nothing more practical than a good theory. Students tend toroll their eyes at this statement and swallow the theory like medicine. Only later, after experience in the field, do they develop a respect for theory. This chapter will put the adapted American city into theoretical perspective, with trust that both understanding and explaining the adapted American city will be made easier with this theory. Finally, theories of institutional dynamics used here should make our study more easily comparative both to other studies of cities and to the processes of change in other formal institutions.