This chapter explores the transnational movements of so called ‘irregular migrants’. We investigate why and how transnational collective action is taken by people in situations of vulnerability and ask how those with limited resources manage to mobilize at the transnational level. In order to frame that core arguments, we analyse one particular event which occurred in 2012, namely the European March of sans-papiers and migrants. We explore how the movement was triggered, how it was organized, what claims were made, and what impact it had. We argue that the movement was subversive in three different ways: irregular migrants sought to act like any other citizen; they questioned the boundaries of the nation state; and they refused to be defined and limited by the global social order. We show that the transnational character of the mobilization is closely related to the root of the problems it sought to address such as European migration policies. Finally, we illustrate how mobilization at a transnational level reinforces the social movements of ‘irregular migrants’.