On October 12th, 2009 Elinor Ostrom received the Nobel Prize in Economics for her analysis of the commons. This article presents a survey of her work. We shall begin by redrawing the academic route of Ostrom. In the second part, we show how she successively used various methods of investigation throughout a route which leaves the meticulous study of multiple concrete situations to evolve towards the design of public policies for big international bodies. The conclusion describes the implications she draws from her work so as to contribute to a renewal of rational choice theory.