Brazil is a country of extreme inequalities, one of the most important of which is the acute concentration of rural land ownership. In recent decades, however, poor landless workers have mounted a major challenge to this state of affairs. A broad grassroots social movement led by the Movement of Landless Rural Workers (MST) has mobilized hundreds of thousands of families to pressure authorities for land reform through mass protest. This book explores the evolution of the landless movement from its birth during the twilight years of Brazil's military dictatorship through the first government of Luiz In cio Lula da Silva. It uses this case to test a number of major theoretical perspectives on social movements and engages in a critical dialogue with both contemporary political opportunity theory and Mancur Olson's classic economic theory of collective action. Ondetti seeks to explain the major moments of change in the landless movement's growth trajectory: its initial emergence in the late 1970s and early 80s, its rapid takeoff in the mid-1990s, its acute but ultimately temporary crisis in the early 2000s, and its resurgence during Lula's first term in office. He finds strong support for the influential, but much-criticized political opportunity perspective. At the same time, however, he underscores some of the problems with how political opportunity has been conceptualized in the past. The book also seeks to shed light on the anomalous fact that the landless movement continued to expand in the decade following the restoration of Brazilian democracy in 1985 despite the general trend toward social-movement decline. His argument, which highlights the unusual structure of incentives involved in the struggle for land in Brazil, casts doubt on a key assumption underlying Olson's theory.