This paper rethinks Marx and Engels’ comments on imprisonment and capitalism. While there has been a tendency to suggest the authors’ comments on crime and punishment were peripheral and secondary to their major projects, such as Marx’s Capital, this paper claims, in fact, their writings on incarceration were guided by their shared theoretical project which included historicizing systems of punishment as correlating with modes of production. Also, while more has been written on their ideas of criminality, instead, this paper excavates their thoughts on prisons, which have often been neglected. Overall, it shows there has been a tendency to underestimate the ways the authors viewed prisons as an important disciplinary mechanism for class control, and a part of the capitalist state more generally. Their work provides an important conceptual foundation for critical sociological perspectives on incarceration.