The size of non-hukou migrants, which is the vantage point for understanding China’s post-reform socioeconomic dynamics driven by migration and urbanization, is affected by the definitional complexities. This chapter provides an in-depth understanding of non-hukou migrants whose numerical data are not readily apparent in making meaningful sense. It discusses the specifics of statistical variables used by various bureaucracies to define non-hukou migrants and the interrelation between the political economy of migration and changes in the administration of non-hukou migrants, which lead to definitional complexities. We argue that, on the surface, a substantial part of the numerical difference is statistical artifact arising from different definitions. Moving from beyond a statistical point of view, the interpretation of various non-hukou migrant definitions has to be conceptualized within the political economy of migration in transitional China that necessitates the persistence as well as changes in migrant control.