In this dissertation, I investigate how online social interactions and user-generated content affect sellers and consumers in online platforms. I conduct three empirical studies to understand the effect of user-generated content in three different types of online platforms: (1) an e-commerce marketplace, (2) an online reviews platform, and (3) an online health community. In study one, I examine how social features (e.g., following others, sharing others’ products) within an electronic commerce marketplace affect status and sales for sellers. This essay contributes to the literature on electronic commerce by deepening the understanding of online social processes among sellers. In study two, I explore how humorous appropriation of an online review platform affects purchase intention and consumer engagement. Utilizing both controlled experiments and analysis of real-world reviews, I demonstrate that humorous appropriation attenuates the effect of review valence on purchase intentions and increases consumer engagement. In study three, I investigate how community ratings are related to patient treatment evaluations and compliance in an online health community. I find that community ratings are positively associated with treatment evaluations and compliance. Moreover, I find that community size and ratings variance moderate the effect of community ratings on treatment evaluations and compliance. Taken together, these essays contribute to the literature on Information Systems by augmenting the understanding of the effects of different types of user-generated content on social (status, engagement, and evaluations) and economic outcomes (purchase intentions and sales). The studies also offer insights for strategic decisions regarding user-generated content in online platforms. / Business Administration/Management Information Systems