Abstract. Securitization of immigration, the rise of interior immigration policing, and forces of carceral privatization have occasioned a remarkable expansion of immigrant detention throughout the United States. Previous studies have drawn attention to the importance of the daily rates paid by the federal government to individual facilities in driving the emphasis on detention. This paper, in contrast, argues that tracing the political and economic geography of money inside detention facilities is also critical for understanding detention expansion and its consequences. We define the processes, mechanisms, and practices of generating profit above and beyond the "per-bed" daily rate as "internal micro-economies" of migrant detention. Drawing on an ongoing examination of migrant detention facilities in the greater New York City metropolitan area, we identify four micro-economies evident in detention facilities: the commissary systems, phone and other forms of communication, detainee labor, and detainee excursions outside detention. These economies show how detained migrants' needs and daily routines are tailored in ways that produce migrants as both captive consumers and laborers. Recognition of multiple micro-economies also highlights the fact that the numbers of individuals and entities invested in the incarceration of immigrants proliferate in tandem with the objectification of detainees. The paper further suggests that attending to relationships embedded in the inner workings of detention exposes economic links across carceral boundaries, rendering visible the porosity between government, private companies, and publics.