Migration patterns are significantly shaped by migration-related policies, which can either restrict or facilitate mobility. One of the most influential policies is China’s hukou system, established in the late 1950s and still in effect today. Over the decades, the hukou system has undergone continuous reforms, playing a central role in shaping internal migration. This chapter provides a comprehensive review of the hukou system and its impact on migration. It traces the evolution of hukou policies across five stages—strict control before 1980, initial relaxation in the 1980s, progressive relaxation in the 1990s, differentiated relaxation in the 2000s, and further differentiated relaxation in the 2010s—and analyzes the rationale and characteristics of each reform stage. It then examines how these changes have reshaped internal migration patterns, influencing migration scale, patterns, and population composition, as well as the motivations and meanings of migration. The chapter concludes by offering insights for future research on the hukou system and its impact on migration.