This paper synthesizes insights from new global data on the effectiveness of migration policies. It investigates the complex links between migration policies and migration trends to disentangle policy effects from structural migration determinants. The analysis challenges two central assumptions underpinning the popular idea that migration restrictions have failed to curb migration. First, post-WWII global migration levels have not accelerated, but remained relatively stable while most shifts in migration patterns have been directional. Second, post-WWII migration policies have generally liberalized despite political rhetoric suggesting the contrary. While migration policies are generally effective, “substitution effects” can limit their effectiveness, or even make them counterproductive, by geographically diverting migration, interrupting circulation, encouraging unauthorized migration, or prompting “now or never” migration surges. These effects expose fundamental policy dilemmas and highlight the importance of understanding the economic, social, and political trends that shape migration in sometimes counterintuitive, but powerful, ways that largely lie beyond the reach of migration policies.