A priest is a person authorized to perform the sacred rituals of a religion, especially as a mediatory agent between humans and deity(s). They also have the authority or power to administer religious rites; in particular, rites of sacrifice to, and propitiation of, a deity or deities. Their office or position is the priesthood, a term which also may apply to such persons collectively.

Priests and priestesses have existed since the earliest of times and in the simplest societies. They exist in all or some branches of Judaism, Christianity, Shintoism, Hinduism and many other religions. They are generally regarded as having positive contact with the deity or deities of the religion to which they subscribe, often interpreting the meaning of events and performing the rituals of the religion. Priests are leaders to whom other believers will often turn for advice on spiritual matters.

In many religions, being a priest or priestess is a full-time position, ruling out any other career. In other cases it is a part-time role. For example in the early history of Iceland the chieftains were titled goði, a word meaning "priest". As seen in the saga of Hrafnkell Freysgoði, however, being a priest consisted merely of offering periodic sacrifices to the Norse gods and goddesses; it was not a full-time role, nor did it involve ordination.