We review the psychology of why information spreads, or the psychology of “virality.” Our review suggests that similar types of information tend to spread like a virus in many contexts—online and offline. This is likely because similar psychological processes drive information spread across contexts. We explain how these psychological processes interact with structural features of information environments—including norms, networks, and incentive structures. In contrast to the idea that information we share reflects our revealed preferences, we argue that widely shared content is often not widely liked—a phenomenon called “the paradox of virality.” We discuss future directions for the psychology of virality, which can use recent advances in artificial intelligence to better understand what goes viral across cultures and contexts.