This dissertation consists of three papers. A common feature of these papers is the interest in how externalities affect consumers and firms’ behavior. In the first paper, I study one type of contractual externalities called exclusive dealing, whereby one firm cannot deal with the competitors of the other. More specifically, I propose and estimate an empirical structural model to investigate the effects on prices of upstream mergers in markets with exclusive dealing contracts. The second paper is concerned with markets for a good with network externalities, i.e. a good that generates higher utility the higher the number of consumers purchasing it. The third paper studies externalities of investments on quality improvement. When more than on...