The book aims at creating the foundations for a broad framework of a theory of mobility in space and time . Starting from a confrontation between mainstream international economics and empirical observation, the approach takes into account the heterogeneity of more or less mobile agents, forms of interaction that go beyond price interaction as well as the dimensions of space and time. It is emphasized that only an interdisciplinary approach that is open to new methods will be able to offer explanations for the spatial dynamics of our times. This approach goes beyond the traditional distinction of national versus international transactions. It is a completely new conceptual framework that makes the integration of traditional approaches as well as future theoretical developments possible.