The first chapter of the thesis studies the advertising competition on the French broadcast TV market. We use a unique dataset on the French broadcast television market including audience, prices, and quantities of advertising of twenty-one TV channels from March 2008 to December 2013. We specify a structural model of oligopoly competition and identify the shape and magnitude of the feedback loop between TV viewers and advertisers. We also implement a simple procedure to identify the conduct of firms on the market. We find that the nature of competition in the French TV advertising market is of the Cournot type. Further, we provide empirical evidence that the price-cost margin is not a good indicator of the market power of firms operating o...