We consider dynamic competition among platforms in a market with network externalities. A platform that dominated the market in the previous period becomes "focal" in the current period, in that agents play the equilibrium in which they adopt the focal platform whenever such equilibrium exists....

This paper studies social-tie formation when individuals care about the geographical location of other individuals. In our model, the intensity of social interactions can be chosen at the same time as friends. We characterize the equilibrium in terms of both social interactions and social...