sellers shape the market structure in platform industries. If product market competition is tough, sellers avoid competitors … single platform emerges, and platforms fight for the dominant position. These insights give rise to novel predictions. For … instance, market concentration and fees are negatively correlated in platform industries, which inverts the standard logic of …

This paper develops a fairly general model of platform competition in media markets allowing viewers to use multiple … affect the viewer composition and thereby the resulting value of a viewer for the other platform. We label this form of … competition "either or both." A central result is that platform ownership does not affect advertising levels, despite nontrivial …