This book gives a comprehensive survey and complete mathematical development of the theory of multi-product oligopolies. Existence and uniqueness of the Nash-Cournot equilibria as well as its stability are analysed for the multi-product Cournot model and for its variants such as labor-managed industries, saturated markets, rent-seeking oligopolies and presence of production adjustment costs. Applications are discussed for network oligopolies, taxation, water resources management, and international fishery. The controllability of multi-product Cournot markets is also briefly analysed.