The Dionysian Mysteries were a ritual of ancient Greece and Rome which sometimes used intoxicants and other trance-inducing techniques to remove inhibitions and social constraints, liberating the individual to return to a natural state. It also provided some liberation for men and women marginalized by Greek society, among which were slaves, outlaws, and non-citizens. In their final phase the Mysteries shifted their emphasis from a chthonic, underworld orientation to a transcendental, mystical one, with Dionysus changing his nature accordingly. By its nature as a mystery religion reserved for the initiated, many aspects of the Dionysian cult remain unknown and were lost with the decline of Greco-Roman polytheism; modern knowledge is derived from descriptions, imagery and cross-cultural studies.

Mystery religions, mystery cults, sacred mysteries or simply mysteries, were religious schools of the Greco-Roman world for which participation was reserved to initiates (mystai). The main characterization of this religion is the secrecy associated with the particulars of the initiation and the ritual practice, which may not be revealed to outsiders. The most famous mysteries of Greco-Roman antiquity were the Eleusinian Mysteries, which predated the Greek Dark Ages. The mystery schools flourished in Late Antiquity; Emperor Julian, of the mid 4th century, is believed by some scholars to have been associated with various mystery cults—most notably the mithraists. Due to the secret nature of the school, and because the mystery religions of Late Antiquity were persecuted by the Christian Roman Empire from the 4th century, the details of these religious practices are derived from descriptions, imagery and cross-cultural studies. Much information on the Mysteries comes from Marcus Terentius Varro.