Jeffrey Kaplan has been one of the most influential scholars of new religious movements, extremism and terrorism. His pioneering use of interpretive fieldwork among radical and violent subcultures opened up new fields of scholarship and vastly increased our understanding of the beliefs and activities of extremists. This collection features many of his seminal contributions to the field alongside several new pieces which place his work within the context of the latest research developments. Combining discussion of the methodological issues alongside a broad array of case studies, this will be essential reading for all students and scholars of extremism, religion and politics and terrorism.