Monopoly Markets
A monopoly is a market situation where there is only one seller.
See Monopoly for more info.
Duopoly Models
A duopoly is a market situation where there are two sellers, for each set of actions and reaction of the duopolist, there corresponds a solution. Thus there is no unique solution for duopoly equilibrium. The solution depends on the actions of one duopolist and the counter of another duopolist.^duopoly-definition
Consider some important Duopoly models: