This literature review examines cross-disciplinary work on radicalization to situate, historicize, frame, and better understand the present concerns around online radicalization and far-right extremist and fringe movements. We find that research on radicalization is inextricably linked to the post-9/11 context in which it emerged, and as a result is overly focused on studying the other. Applying this research to the spread of far-right ideas online does not account for the ways in which the far-right’s endorsement of white supremacy and racism holds historical, normative precedent in the United States. Further, radicalization research is rife with uncertainties, ranging from definitional ambiguity to an inability to identify any simplistic, causal models capable of fully explaining the conditions under which radicalization occurs. Instead, there are multiple possible pathways to radicalization, and while the internet does not cause individuals to adopt far-right extremist or fringe beliefs, some technological affordances may aid adoption of these beliefs through gradual processes of socialization. We conclude that the term “radicalization” does not serve as a useful analytical frame for studying the spread of far-right and fringe ideas online. Instead, potential analytical frameworks better suited to studying these phenomena include theories prominent in the study of online communities, conversion, mainstreaming, and sociotechnical theories of media effects.