Cournot duopoly is an oligopoly with the following features: (i) there is two firms producing an homogeneous product; (ii) firms have market power; (iii) firms compete in quantities, and choose quantities simultaneously; (iv) there are barriers to entry; (v) there is strategic behavior by the firms; (v) firms do not cooperate. The Cournot-Nash equilibrium is the Nash equilibrium applied to the Cournot model.