In two-sided markets, two groups of agents interact through platforms. Because agents’ decision to join a platform is affected by the presence of agents on the other side, their interactions create indirect network externalities and make platforms’ strategies different from those of firms in one-sided markets. In this paper, I use a structural model to show that platforms may take a loss on one side of the market to make a profit on the other side and that platform mergers may benefit some agents by lowering prices or attracting more agents on the other side of the market.