The rationality assumption has been the center of neo-classical economics for more than half a century now. In recent years much research has focussed on models of bounded rationality. In this thesis it is argued that both full and bounded rationality can be used for different kind of problems. In the first part full rationality is assumed to analyse technology adoption by firms in a duopolistic and uncertain environment. In the second part, boundedly rational models are developed to study the evolution of market structure in oligopolistic markets as well as price formation on (possibly) incomplete financial markets. The third part of the thesis presents an alternative to the framework of Transferable Utility games in cooperative game theor...