Protected areas, under 19 different statuses, cover almost 41% of the surface area of Brazil's Amazon region. As conservation areas, they are used by the state as a tool of land blocking which is supposed to prevent economic ventures, and therefore subsequent deforestation (Léna 2005)1. The inhabitants of these protected areas, when their presence is tolerated, are thus ascribed a stereotypical social immutability, as is often the case with so-called traditional societies. Yet, on the contrary, we could regard the capacity of these societies to constantly adjust their relationships to the natural environment and to social others, both locally and in a wider interethnic context, as enabling inhabited protected areas to play a significant role in the conservation of the environment. In this perspective, when the actors of social change manage collectively to control its dynamic, this can become a guarantee of environmental conservation. To illustrate this point, we present in this chapter a study of two Amerindian groups from the Brazilian Amazon taking as examples the villages of Apiahiki and Moikarakô, respectively situated in the Yanomami and Kayapó indigenous lands. The territories of these two groups, traditionally unbounded, were recently marked out and legalised in the form of specific protected areas known as 'Indigenous Lands' (Terras Indígenas). On analysing the historical process which led to the official recognition of these areas, we were able to assess some aspects of the impact that such a transformation had on the local indigenous management of space and resources of the tropical forest. Through these examples, we try to highlight the way in which Amerindian societies invent forms of 'sustainable development' satisfying at the same time their own values and the exogenous demand for the conservation of their lands as protected areas.