This article argues for recognition of fringe fluidity as a distinct radicalization pathway. Most studies on individual-level radicalization examine how relatively normal people come to accept violent extremist beliefs. But some people who come to accept and act on an extremist ideology transition from the embrace of one form of violent extremism to another—and understanding their prior extremism is essential to appreciating their ultimate beliefs and actions. The article demonstrates the existence of fringe fluidity by detailing the pathway between neo-Nazism and militant Islamism. Factors allowing fringe fluidity between these ideologies include recent cases of individuals who transitioned from one to the other or simultaneously embraced both; some ideological overlap, particularly in shared out-groups; and historical precedent that allows some adherents to reconcile inconsistent aspects of the two ideologies. Despite this article’s focus on neo-Nazism and militant Islamism, fringe fluidity is likely more widely applicable beyond the context of these two ideologies.