Why were the Mexican and United States governments unable to establish formal cooperation for the management of migration flows even after agreeing on the need for a “shared responsibility” approach and establishing an agenda for negotiations on a bilateral agreement in the spring of 2001? Conventional wisdom is that the terrorist attacks of September 11th were the main reason for the shift from a bilateral to a unilateral approach to the management of US-Mexico migration flows. Although this event changed the US government’s foreign policy priorities, in order to understand the reasons why the proposal for a migration agreement failed, it is necessary to look beyond the security context that permeated the US agenda after September 11th and analyse the underlying structural, domestic and ideological factors that influenced the governments’ positions during and after the negotiations. By examining the context of power asymmetry in the US-Mexico relationship, the domestic politics that surround the issue and public perceptions of immigration in the United States, this paper identifies the challenges implied in efforts to expand bilateral cooperation over migration issues in the NAFTA framework. The fact that both countries’ migration policies are mostly pursued unilaterally despite the acceptance of a “shared responsibility” raises key questions regarding the limits of regional integration and bilateral or multilateral cooperation for the management of migration.