This paper addresses interagent interactions, an issue that has received limited attention in travel behavior research. Drawing upon the theory of externalities and the sociological notion of social networks, we develop a discrete choice model that incorporates elements of social influence in addition to more conventional factors such as the attributes of alternatives and the characteristics of decisionmakers. Using simulation, we apply the model to the case of telecommuting—that is, the decision to telecommute or not—over two waves. The experiment suggests that some marginal adopters of telecommuting are influenced heavily in the second wave by the decisions of others in the first wave. Furthermore, the example illustrates the importance of social influence on new adopters of telecommuting in the second wave.