This chapter borrows insights from the extant literature on the far right and the broader literatures on political parties, social movements and militant democracy to develop a theory of local party development. It explicates a theoretical framework examining how endogenous and environmental factors shape the development of extremist right-wing party organizations, at the national and, more importantly, at the subnational level. It first looks at how internal party characteristics shape the capacity of extremist right-wing parties to grow roots in local societies. It then focuses on environmental factors: it examines how electoral, institutional and societal factors affect local party trajectories.