The question as to why individuals join extremist groups, radicalize or even go on to commit acts of terror have been a focus of research for many decades and a multitude of researchers from different disciplines have advanced theories and hypotheses in an attempt to provide an answer. The German literature on the topic has also offered a number of promising contributions worth discussing in the context of general international literature. We begin by examining factors pertaining to the individual as such (personality features, cognitions and emotions) and then move on to address theories that focus on the interaction between individuals and their social environment and long-term socialization processes.