Fixed point theorems state what criteria must be met for a mapping of a set to itself in order to keep some points of the set unchanged. The object of this work is the study of these important Theorems and their analysis with the help of their applications in various fields of mathematics. The first chapter lists some basic definitions and some suggestions that we be used later. In the following chapters we will see the theorems of Banach, Schauder, Krasnoselskii and Kakutani for a fixed point. Τhe last chapter concerns the application of Kakutani's fixed point theory to the significant Nash game theory in a n player game.