This dissertation explores the spread and articulation of Garveyism—the political movement spearheaded by Jamaican activist Marcus Garvey—across Africa, the greater Caribbean, and the United States in the years following the First World War. Scholarship on Garveyism has remained fixed within a conceptual framework that views the movement synonymously with the rise and fall of Garvey's organization, the Universal Negro Improvement Association (UNIA), and which focuses predominantly on the activities of the organization in the United States. This study argues that Garveyism is more fully rendered as a global endeavor of network-building, consciousness-raising, and activism that extended beyond the operational parameters of the UNIA, influenced a diverse array of regionally-constituted political projects, and nurtured the flowering of a profoundly "Garveyist" period in the history of the African diaspora. It did so by sustaining and disseminating a thrilling vision of international politics that suggested the inexorable liberation of the world's "colored" majority; by offering its followers a powerful diasporic identity within which to project their aspirations and negotiate extant relations of power; and by providing a flexible framework within which organized communities could react to local conditions and opportunities. This work was manifested in the persistence of local UNIA divisions in the United States, particularly in the rural South, and in the development of a regional mode of postwar labor politics in the greater Caribbean. In Africa, Garveyist organizing helped facilitate challenges to colonial regimes in a variety of guises, including millennial religious revivals, "Welfare Association" politics, and the politics of tribal representation. The Age of Garvey was defined not by the spectacle of the UNIA—its shipping lines, colonization schemes, and boisterous international conventions—but by the comparably mundane work of organization and preparation being done behind the scenes. By sustaining vibrant containers of locally-controlled, diasporically-framed, and mass-based politics, Garveyites provided a training ground for a rising generation of activists. And they nurtured a rich organizational network that laid the foundation for the titanic struggles against domestic inequality, colonial domination, and economic exploitation that followed.