This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book illustrates the dynamics of spacing and timing urban development, where the spatial form of the city is the result of a variety of social, economic and political processes. It assesses the changes occurring from a densification process in an already dense urban area with a case study of an inner city district in Copenhagen. The book demonstrates that a densification process actually takes place in the district. It also discusses changes in urban planning in the Netherlands. The book analyses how the function of planning in a Swedish town has changed over time. It focuses on the problem of adapting the administrative level to the spatial scale of the problems. The book also describes the spatial, functional, environmental and social consequences for the local environment, and discusses the planning system and its ability to cope with such processes.