Until the 1980s, deforestation in the Brazilian Amazon had largely been the result of public policies (incentives, investment). Since the 1990s, with basic infrastructure installed and cattle-ranching turned profitable due to innovations, deforestation has relied on its own endogenous dynamics. To stop this trend, politics will have to use both traditional and modern instruments for influencing economic behaviour, that is, control and sanctions as well as dialogue and negotiation. Since democratisation, civil society organisations (CSOs) have grown in the Amazon region, often with important support from foreign non-governmental organisations (NGOs). Today, they are important partners for sustainable, bottom-up development strategies. This has become evident in the political mobilisation against two large public infrastructure investment projects: the dam and hydroelectric plant of Belo Monte; and the paving of the federal highway BR-163 between Cuiabá and Santarém. This article explores how local CSOs perceive these projects, what importance they assign to the environmental dimension and what alliances they build with other, local, national and international actors in order to achieve their objectives. © 2005 Taylor & Francis.