The main objective of this systematic review is to synthesize the empirical evidence on how the Internet and social media may, or may not, constitute spaces for exchange that can be favorable to violent extremism. Of the 5,182 studies generated from the searches, 11 studies were eligible for inclusion in this review. We considered empirical studies with qualitative, quantitative, and mixed designs, but did not conduct meta-analysis due to the heterogeneous and at times incomparable nature of the data. The reviewed studies provide tentative evidence that exposure to radical violent online material is associated with extremist online and offline attitudes, as well as the risk of committing political violence among white supremacist, neo-Nazi, and radical Islamist groups. Active seekers of violent radical material also seem to be at higher risk of engaging in political violence as compared to passive seekers. The Internet's role thus seems to be one of decision-shaping, which, in association with offline factors, can be associated to decision-making. The methodological limitations of the reviewed studies are discussed, and recommendations are made for future research.