Many of the arguments behind efforts to reform this nations's immigration laws allege that immigrants, especially illegal immigrants, take jobs away from native workers, depress wages, and receive public services valued in excess of their tax contributions. To provide a basis for appraising these economic arguments, this paper presents a model for simulating the economic effects of immigration. The model is a theoretical framework, useful for understanding how the various economic responses triggered by immigration relate to one another. Simulation of the model shows that the effects of an increase in annual flow of immigrants are highly sensitive to the substitutability between labor and capital and among different kinds of labor; to the responsiveness of wage changes to unemployment; to the presence or absence of wage rigidity; and to the skill mix of immigrants. Effects are also sensitive to regional behavior, specifically to the response of interregional migration and interregional trade to wage and price differentials. The report contains an overview of the model, simulation of the model, and an agenda for future work on the model. Included are a list of references and related titles. An appendix lists the variables, the equations with the coefficients used for the reference simulation, and the alterations for each of the other simulations. (LBW)