This literature review summarizes findings from 63 articles published between 2001 and 2020 that study discretion of frontline workers at migration control. The results demonstrate that discretionary practices in various migration control situations (e.g., border zones, migration agencies, courts, public welfare services, and detention centers) are widespread but share common patterns. Frontline workers’ racialized prejudices and perceptions of migrant deservingness were the most dominant patterns found in the data, although there were some disagreements about which were most influential. Discretion of frontline workers was described as foremost detrimental to migrants, as it amplified the migrants’ vulnerable situations, even if it occasionally could increase individual migrants’ room for agency and strategic maneuvering. Contrary to the assumption underpinning the control gap-thesis in immigration policy literature that governments’ capacity to control migration is hampered by the significant discretion at the frontlines, many studies in our sample describe how governments shape the discretionary practices of frontline workers through informal, subtle, and opaque governing strategies. These informal governing strategies enable central governments to deflect responsibility for discriminatory and inhumane policy outcomes.