Regionalism was a defining feature of Greek society in all periods of antiquity. The implications of this regionalism for the history of religion are crucial: No two areas of the Greek world worshipped the same pantheon of gods in the same way. Regional variation was the norm. This dissertation focuses on Thessaly, a large frontier area of mainland Greece which has yet to receive systematic attention in the field of history of religion, and analyzes its regional cults. By regional cult, I mean those cults which are attested in more than one place in Thessaly but do not have a near-panhellenic distribution outside of Thessaly. The problem is approached through a detailed study of the available literary, archaeological, numismatic and epigraphic sources. After providing an outline of major currents in Thessalian social and political history, I consider in succession the Thessalian calendar, Thessaly?s ?federal? sanctuaries and other regional cults. Thessaly is found to be home to a wide variety of idiosyncratic cults, including: Apollo Kerdoios, Apollo Leschanorios, Artemis Throsia, Athena Itonia, Dionysus Karpios, Ennodia, Poseidon Petraios, Themis, Zeus Eleutherios, Zeus Homoloios and Zeus Thaulios, among others.