This chapter analyses the formation of diasporas akin to the emergence and development of social movements. It presents the dominant canon of the political process theory, which was primarily based on the reform movements of US citizens in the 1960s onwards. Despite criticisms, the political process theory remains the hegemonic framework in social movement scholarship. The chapter discusses mechanisms and processes that recur across a wide range of contentious politics, in the tradition of McAdam et al. and other scholars who have advanced the research agenda of Dynamics of contention. Due to the limitations of social movement theories in explaining mobilizations that challenge nation-state-based citizenship, it explores ideas from long-distance nationalism and migrant political transnationalism to account for a full range of variations within social movement concepts. Like other social movements, diaspora mobilization as a transnational political project stems from the interplay of opportunities and threats, resources in the community, and strategic deployment of ideologies and identities.