As the world?s population is increasingly concentrated in urban centres, urban systems analysis has become a critical field of research ? one that overlaps the traditional academic territories of geography, economics, and regional science. John Marshall defines urban systems analysis as a study of the spatial organization of networks of urban centres at regional, national, and international scales. In this introduction to the subject he presents a framework for its study.Marshall maintains that the study of the structure and development of urban systems should be guided by a principle-based framework in which the themes of location, economic functions, and population size are in the foreground. He outlines how urban systems analysis seeks to provide ?insight into the roles performed by urban centres as elements of the gran process of settlement and development of the earth by humankind.?