The impact of freedom of movement in the EU on the restructuring of national social citizenship has been subject to vigorous debates in both political and academic discourses. This chapter draws on the insights of critical citizenship theory to move beyond the individualistic approach to transnational rights in liberal cosmopolitanism, on one hand, and the static approach to solidarity in defence of national closure, on the other. Rather than a fixed collection of social rights and a finalised national project, social citizenship can be understood as an open-ended process shaped by ongoing collective struggles over needs and social inclusion. Relations of solidarity and reciprocity can emerge in such processes rather than being a precondition external to them. The chapter then considers the political significance of non-institutionalised forms of contestation over the social rights of migrants that resist and challenge the individualist and discriminatory logics in the governance of free movement. As practices geared towards constructing new solidaristic relations and identities across borders, these acts of (social) citizenship articulate an alternative understanding of mobility as social and spatial practices that enable collective engagements and set in motion inclusive forms of solidarity that traverse the boundaries of the national, the European and the legal.