This book intends to familiarise the reader with the political and sociological thought of Florestan Fernandes, covering the range of his research themes and socialist militancy between the 1940s and 1990s.Considered the founding father of sociology in Brazil, Florestan Fernandes' work is essential for an understanding of the historical and political dilemmas of Brazilian and Latin American societies. His main themes encompass research on folklore, indigenous peoples, race relations between blacks and whites, sociological theory, education, underdevelopment, dependence, Latin American dictatorships and the Brazilian "re- democratization" after 1980, providing a new interpretation of Latin America from the point of view of the lumpen social strata.Following Mannheim's inspiration, the present work is inserted in the field of sociology of knowledge. It takes an original approach to the ideas of Florestan Fernandes based on the notion of a lumpen thought style. This book is a key resource for readers learning about the history of the social sciences in Latin America, and about the political dilemmas of Latin American societies.