We evaluate the empirical evidence interrogating the question of whether social media erodes social cohesion. We look at how networks, information exchange, and norms operate on these platforms. We also evaluate the conditions under which social media can be conducive to forming social capital and encouraging prosocial behavior. We discuss the psychological mechanisms that operate at the individual level and assess whether social media can create the environment and incentives to sustain cooperation and constructive exchange. Our discussion of the literature centers on how attitudes, perceptions, and beliefs are formed during the type of online interactions encouraged by platforms, their design, and affordances. We consider the policy implications of existing research, focusing on how empirical studies may inform regulatory efforts and platform interventions.Social media platforms like Twitter, Facebook, and Reddit have changed how we consume and use information. These platforms decentralize content curation, allow selective exposure to like-minded sources, and offer loose moderation policies to govern interactions. Users can circumvent traditional gatekeepers of information and forge new forms of collective action. Social media platforms have also created an environment prone to conflict, polarization, incivility, and information disorders. In the past few years, social media platforms have been pushed to the spotlight of high-profile discussions that aim to identify (and, ideally, remedy) the threats these platforms currently pose to democracy (Haidt, 2022;Vaidhyanathan, 2018).But how much do we know about social media's role in weakening democracies and undermining social cohesion? Most popular treatments of social media and social cohesion are based on anecdotes and, at best, correlational data. Do social media merely reflect larger societal trends, or is there something specific to these platforms that creates or aggravates conflict? Do the effects of social media vary by platform or the affordances within platforms? The goals of this review are (1) to evaluate existingThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.