The mobility of sportsmen and women, like that of professional entertainers, is a neglected but important theme in social and cultural history. Focusing on the transatlantic migration stream between the United States and Britain, and on three sporting case studies (association football, boxing, and speedway racing), this article demonstrates that patterns of sporting migration were rooted in wider migration systems and that regulatory responses were embedded in the broader policies of governments, governing bodies, and trade unions. Like many other migrant workers, athletes faced considerable restrictions between the wars. Yet, in the context of the increasing internationalization of sporting competition, and an emerging interconnection between national sporting cultures, interwar sport also offered new and unprecedented opportunities for mobility and for the construction of transnational sporting stars. Drawing on a range of archival sources, this article provides a fresh perspective on both the character of international migration and the tensions between transnational and national identities between the wars.