Internet users are constantly confronted with metric information about the popularity of goods, services, and content. These popularity cues (PCs)—which we define as metric information about users’ behavior or their evaluations of entities—serve as social signals for users who are confronted with them. Due to the high relevance that PCs have for organizations, consumers, and scholars, this article provides a systematic overview of PC research. First, we present a theoretical conceptualization for the effects of PCs. Second, we analyze empirical research that focuses on PCs by providing a review of academic, peer-reviewed studies on the direct effects of PCs in online media (N = 61). Third, we utilize the results of our literature review to address current shortcomings in the literature and to provide insights for future research.