This article critically reviews theories of migration policy according to two criteria: methodological rigor and explanatory plausibility. It finds that political economy accounts are theoretically robust, but at the price of oversimplification. Neo-institutional theories offer more sophisticated accounts, but fall short on a number of methodological and explanatory counts. As an alternative, this article suggests a theory focusing on the functional imperatives of the state in the area of migration, which shape its responses to societal interests and institutional structures.Recent literature on the theory of migration policy has tended to be dominated by two overlapping themes: the question of why migration policies fail; and attempts to explain the inclusionary tendency of migration and integration policies. While the two issues are often treated together -and may indeed be similarly theorized -they are in principle separable. The first deals with the gap between (proclaimed) policy objectives and outcomes. It seeks to explain why states fail to achieve the goals set out in their stated migration policies (Hollifield, 1986(Hollifield, , 2000Castles, 2004; Cornelius et al. , 1992:3). The second theme is concerned with explaining the gap between the generally protectionist bent of public opinion in democratic states, and the more inclusionary policies that often emerge. While this may be understood as one dimension of the policy failure issue, it does in fact raise a rather different set of questionsquestions which may be obscured if we treat it as a subset of the first theme. Posing the question this second way implies a more narrow focus on the configuration of interests, ideas, and institutions that shape policy. It also allows us to address more specifically the question of why migration policy in liberal states does not succumb to the pressures for closure apparently endemic in democratic and welfare state systems (Bommes and Geddes, 2000;Hollifield, 2004).While there are any number of theories for explaining the first gap, recent attempts to theorize the second have been dominated by two schools: neoclassical political economy, as exemplified in the work of Gary P. Freeman; and various 1 Many thanks to Michael Bommes, Gary Freeman, James Hollifield, Mark Miller, and the anonymous reviewers at IMR for their very helpful comments on earlier drafts of this paper.