Why have dominant parties persisted in power for decades in countries spread across the globe? Why did most eventually lose? Why Dominant Parties Lose develops a theory of single-party dominance, its durability, and its breakdown into fully competitive democracy. Greene shows that dominant parties turn public resources into patronage goods to bias electoral competition in their favor and virtually win elections before election day without resorting to electoral fraud or bone-crushing repression. Opposition parties fail because their resource disadvantages force them to form as niche parties with appeals that are out of step with the average voter. When the political economy of dominance erodes, the partisan playing field becomes fairer and opposition parties can expand into catchall competitors that threaten the dominant party at the polls. Greene uses this argument to show why Mexico transformed from a dominant party authoritarian regime under PRI rule to a fully competitive democracy.