Abstract : Steppe at the end of the southern world, swept by the winds, made of contrasts, dramas, hopes and legends; Patagonia is also a territory where several groups of indians hunters lived in. In a few decades, between the end of 19th and the beginning of the 20th century, they were decimated to leave the place to the sheep breeders paid by wool companies. In less than one century, the sheep-farm-induced mismanagement of the grasslands would have been the main motor of the fast and irreversible degradation of the Patagonian ecosystems. However, the analysis of the agrarian history of Patagonia seems to show that the replacement of the guanaco by the sheep and the Tehuelche hunter by Basque shepherd is less the cause of this ecological catastrophe than the result of a process of colonization in which the public policies seem to have played an important role. To understand the past and present dynamics of this process may help to the development of prospective scenarios and thus with the management of the territorial development. From this point of view, the objective of this thesis is better to determine the roles and modes of intervention of the sheep farming in the colonization of Patagonia and the construction of its identity.