This chapter conceptualizes and classifies extremist right-wing parties by identifying their similarities to and differences from radical right-wing parties. It first produces a conceptual framework for identifying the two subgroups of the far right. Borrowing from existing literature on party families, it examines how various criteria such as the ideology, program, electorate, origins and international links of political parties can help distinguish between these two subfamilies. It then adds an important criterion this literature ignores, the type of political action parties undertake. Using this conceptual framework and the various criteria, the chapter then proceeds to the classification of forty-one parties in thirty countries.