Taking on Goliath analyzes the formation and decline of the most successful opposition party challenge to Mexico's long-ruling Institutional Revolutionary Party (PRI), which, until 1988, had ruled unchallenged for more than sixty years. The emergence of this new left opposition in 1988 shattered the myth of PRI invincibility. However, its failure to capitalize on its initial success raises intriguing questions about the relationship between party creation and consolidation and about the sources of party system change and democratization.This book is the only major study in English of the origins and trajectory of the PRD, the party that today represents the unified Mexican left. Kathleen Bruhn draws on extensive field research, including interviews of major participants, local case studies of party organization, documentary evidence from party statutes and reports, and newspaper archives, as well as a statistical analysis of the basis of the left vote. The insights Bruhn offers into the different conditions that affect the functioning of political parties in their emergence and in their later consolidation apply broadly to many developing countries, but they especially help us understand the possibilities for greater democracy in Mexico today.