This book studies optimal pricing, variety and commitment by plat-forms operating in markets, which combine a two-sided structure with a vertical relationship. The first essay analyzes the choice of product variety by a two-sided sponsored platform. The second essay studies the existence of pure strategy symmetric price equilibria in a generalized version of Salop (1979)'s circular model of competition between differentiated products, in which consumers are allowed to purchase more than one brand. The third and central chapter of my dissertation proposes a model of Bertrand competition...