Much current literature argues that the Mexican revolution was not a revolution at all, but rather a series of rebellions that did not fundamentally alter the social order. Similarly, many scholars assert the changes in the Mexican work world during the Mexican revolution were the result of a paternalistic state rather than the product of the actions of workers. This article examines cotton textile workers' relationship to authority in the workplace during the most violent phase of Mexico's revolution, 1910–1921. The results suggest that revolution indeed gripped the country, one that energized the country's still emerging factory proletariat. There is compelling evidence that millhands throughout Mexico continuously and successfully challenged the authority of owners and supervisors, fundamentally altering the social relations of work. It is this “hidden” revolution in the factories that explains changes in labor law, labor organization, and worker power in the immediate post-revolutionary period. The effectiveness of the workers' challenge to authority is what explains: 1) the new regime's need to unionize; 2) the development of pro-labor labor law after the revolution; 3) the power of unions after 1920. In short, workers' challenge to authority during the revolution is what explains the labor outcome of the revolution afterwards.