This article introduces the special issue on ‘Understanding Blue Spaces’ which examines relationships between blue spaces, sport, physical activity, and wellbeing. The articles progress conversations across humanities, social sciences and inter-disciplinary areas of research on diverse sporting practices, that span local to trans-national contexts. This collection offers new insights into politics, possibilities, and problems of the role of blue spaces in our wellbeing—individually, socially, and ecologically. In addition to outlining the 10 articles in the SI, which include ocean swimming, surfing, sailing/yachting, and waka ama paddling, we contextualize this work, discussing key thematic areas both across these papers, and in the wider interdisciplinary body of work on blue spaces, wellbeing, and sport. Specifically, we outline the role of physical activities and leisure practices in how we access, understand, experience, and develop relationships to seas and oceans, as well as to self, places and communities of human and non-human others. We also discuss the ways in which particular bodies, individuals, and communities (human and more-than-human) are marginalized or excluded, and the need for understanding concepts such as wellbeing, place, and self beyond dominant European traditions. This SI highlights how localised experiences of blue spaces can be, while emphasising the need to recognize diverse cultural, economic, geographic, sociodemographic, and political factors that contribute to a disconnect with, or exclusion from blue spaces, impacting who can use blue spaces, how they can be used, how they can be researched, and how power is reproduced and contested.