This contribution to the Common Knowledge symposium “Fuzzy Studies” explores the boundaries between religions by exploring the ambiguous place of yoga in various religious traditions, both modern and premodern. Recently, certain Hindus and Christians have tried to argue that yoga is an essentially Hindu practice, making their case by appealing to the Yoga Sutras, a text by the Sanskrit author Patanjali. However, on closer examination, the Yoga Sutras seem to exist in a fuzzy, indeterminate space that is not quite “Hindu” in the way the word is understood today. For instance, other Sanskrit authors of the first millennium CE criticized Patanjali's yoga teachings for not being properly theistic and for having strong affinities to Buddhism and Jainism. Yoga was also integrated into at least one of the “religions of the book” in the medieval period: in India in the second millennium, yoga was practiced widely among Sufis, who adapted it in surprising and idiosyncratic ways to make it compatible with their own Islamic philosophies. Nicholson concludes with an appeal for a more nuanced understanding of religious contact that goes beyond the pejorative term syncretism to acknowledge that religious mixing has been a central force in the development not only of Hinduism and Islam, but also of Christianity.