There have been two major classes of urban area models: nonspatial models of income, employment, and structural change; and land use models usually oriented toward transportation planning. Recent efforts have become relatively complicated and have employed quite sophisticated techniques, with particular attention being paid to the housing market. Nevertheless, most of the work done so far appears somewhat deficient; convincing behavioral relations forming the basic structure are absent; and there have been inadequate efforts to test and validate the models. Further, relatively few efforts have specified the institutional framework necessary to introduce policy actions directly, although some recent efforts have been made in this direction. We propose to construct a model of the Boston metropolitan area that contains three major parts: a macroeconomic nonspatial model of output, employment, and income distribution; a model of long-term adjustments of population and capital stocks; and a model of spatial allocation. The equations of the model will be econometrically estimated and the main thrust of our efforts will be devoted to specification and testing of structural relationships reflecting actions of households, busi nesses, and governments interacting within both market and nonmarket institutions. The purpose of building the model is to permit systematic evaluation of a very wide range of policy alternatives considered at national, state, metropolitan, or local jurisdiction levels. If this is to be accomplished, there are three requisites. First, the model must endogenously generate those variables that enter evaluative (social welfare) functions. In this model we consider income, income distribution, availability of public services to particular population groups, and residential segregation of racial and income groups to be such variables. Second, the model must be designed so that policy alternatives can be modelled by varying the levels of particular exogenous variables. Finally, the model structure and parameter estimates must provide a model with a high degree of predictive power if the enterprise is to be of any value for policy evaluation. This paper contains a general guide to our thinking about how to construct and implement such a model. Many crucial questions of specification remain unresolved. To date we have collected most of the data that will be needed for preliminary versions of the model and some equations have been estimated. Undoubtedly many compromises will have to be made between our plans and what * Massachusetts Institute of Technology. This research was supported by a grant from the Ford Foundation.