Mexico stands apart for having been ruled by one political party since the 1920s, and this study examines the remarkable political stability Mexico has experienced over the past seven decades. Cothran argues that the country's unusual stability has been the result of the interaction of six factors: the institutionalized nature of the political system; the effectiveness of the regime in achieving rapid economic growth; the adaptability of the regime to emerging pressures; the cohesiveness of the political elites; the judicious use of coercion; and Mexico's proximity to the United States. However, this historical stability is facing new challenges in the 1990s. The author analyzes the changing political, social, and economic landscape in Mexico, and forecasts whether and how Mexico's semi-authoritarian political system will survive.