While international migration can be studied as a case of international factor mobility in response to factor-reward differences, we can also proceed beyond theories which view immigration in terms of international factor movements.

1. (1) Rather than considering migration only in terms of location responses of apersonal factors of production, we might wish to consider the greater complexities that are introduced by recognition of the personal relationships and characteristics of people.

2. (2) We might wish to consider whether and how national and cultural preferences influence immigration policies.

3. (3) We might wish to view countries' immigration policies as endogenously determined by the self-interest of pre-existing residents.

Such directions of investigation suggest that the economic considerations that are stressed by the theory of international factor movements only partially explain the propensity of national states to control and restrict immigration. For immigration policies are also seen as reflecting cultural preferences and affinities, and perhaps likes and dislikes that are contained in the collective memories of different peoples.

Although these latter considerations add relevant dimensionalities to the study of international migration, incentives derived from comparative incomes retain a primary role in providing a market foundation for international migration. In section 1 we provide a brief overview of international migration, as presented by the theory of international trade and factor mobility (for more comprehensive accounts than we present here, see Wong, 1995, and chapter 2 in this volume), but we observe how differences in policies adopted by countries toward trade and immigration are inconsistent with policy symmetries implied by the theory.