A scientific understanding of urban-metropolitan structure and function is becoming increasingly important for metropolitan planning decisions and for governmental policy development, especially in the field of transportation. There is a strong coincidence between the needs of policy makers for adequate information about the implications of alternatives, and the interest of scientists in explaining the development of cities. Theories of urban form and intra-urban location are examined in some detail. It is concluded that existing theories of urban form are largely descriptive and taxonomic, while existing theories of locational behavior may be inadequate to deal with the inflexibilities and nonlinearities that arise in the urban framework. An adequate explanation and theory of metropolitan growth and structure depends on the accumulation of considerably more knowledge as to the behavior of locational decision makers, and the ways in which metropolitan policy impinges on their decisions. Some of the problems of this analysis are explored. Different types of models applicable to the urban system are considered and the particular model under development at the Penn Jersey. Transportation Study is sketched in relation to criteria developed. The implementation of models of the type discussed is related to questions of data collection, computer technology, mathematical formulation, and other operations-research concepts.