The location of industrial employment is a critical factor in virtually all models of urban spatial structure. However, most theoretical and empirical models of the urban economy say little about the determinants of industrial location. This paper develops a conceptual framework for analyzing the dynamic changes in industrial location and presents tests of several major hypotheses about the determinants of employment location. The empirical analysis models the spatial structure of employment for three selected industries in the Boston metropolitan area for the period 1947 through 1968.