Living on the frontier. Post-transit in Mauritania and Mali This article focuses on the situation of “transit” migrants remaining in the country of transit. Our findings are based on a long-term observation study of Nouadhibou (Mauritania) and Bamako (Mali). Three case studies reveal diverging ways of transforming migration experiences into social capital, while taking advantage of the opportunities offered by life on the frontier. All cases have in common to be connected with transnational networks. These include for instance international trade and religious network in Nouadhibou or a heterogeneous network of migration management and humanitarian aid organizations in Bamako. In the latter, as a counterpoint to the emphasis placed on individual trajectories, we offer an account of collective mobilization and links of solidarity within the ghetto of the so-called “Central Africa deportees”, with a specific focus on its integration into the existing network of illegal migrant associations.