Drawing on historical institutionalism and strategic frameworks, this book analyzes the evolution of the Workers’ Party between 1989, the year of Lula’s first presidential bid, and 2009, when his second presidential term entered its final stretch. The book’s primary purpose is to understand why and how the once-radical Partido dos Trabalhadores (PT) moderated the programmatic positions it endorsed and adopted other aspects of a more catch-all electoral strategy, thereby increasing its electoral appeal. At the same time, the book seeks to shed light on why some of the PT’s distinctive normative commitments and organizational practices have endured in the face of adaptations aimed at expanding the party’s vote share. The conclusion asks whether, in the face of these changes and continuities, the PT can still be considered a mass organized party of the left.