The use of crowdfunding platforms to cover the costs of healthcare is growing rapidly within low-, middle-, and high-income countries as a new funding modality in global health. The popularity of such "medical crowdfunding" is fueled by health disparities and gaps in health coverage and social safety-net systems. Crowdfunding in its current manifestations can be seen as an antithesis to universal health coverage. But research on medical crowdfunding, particularly in global health contexts, has been sparse, and accessing robust data is difficult. To map and document how medical crowdfunding is shaped by, and shapes, health disparities, this article offers an exploratory conceptual and empirical analysis of medical crowdfunding platforms and practices around the world. Data are drawn from a mixed-methods analysis of medical crowdfunding campaigns, as well as an ongoing ethnographic study of crowdfunding platforms and the people who use them. Drawing on empirical data and case examples, this article describes three main ways that crowdfunding is impacting health equity and health politics around the world: 1) as a technological determinant of health, wherein data ownership, algorithms and platform politics influence health inequities; 2) as a commercial determinant of health, wherein corporate influence reshapes healthcare markets and health data; 3) and as a determinant of health politics, affecting how citizens view health rights and the future of health coverage. Rather than viewing crowdfunding as a social media fad or a purely beneficial technology, researchers and publics must recognize it as a complex innovation that is reshaping health systems, influencing health disparities, and shifting political norms, even as it introduces new ways of connecting and caring for those in the midst of health crises. More analysis, and better access to data, is needed to inform policy and address crowdfunding as a source of health disparities.