The overwhelmingly progressive outcome of the Second Vatican Council in the Roman Catholic Church (1962 to 1965) changed Church doctrine on everything from the Latin mass to nuns' habits to openness to other faith traditions. This article examines a cause of this outcome by analyzing the informal organizations activist bishops built during the Council. Progressives' and conservatives' cultural understandings of authority determined what type of organization they built as well as how effectively that organization helped them to address their concerns. Progressives believed in the doctrine of “collegiality,” that bishops convening together are as infallible as the Pope—a doctrine conservatives saw as threatening the primacy and authority of the Pope. Consequently, while progressives built a highly effective, consensus-based organization as soon as the Council began, conservatives were much slower to mobilize and, when they did so, formed a hierarchical organization that proved to be much less effective. Most studies of social movements do not have faith in the effectiveness of the progressives' consensus-based organization, which have typically found such organizations to be inefficient and subject to breakdowns. This study suggests that organizational effectiveness depends in part on how well activists' cultural understandings mesh with the environment in which they are enacted.