The Introit (from Latin: introitus, "entrance") is part of the opening of the liturgical celebration of the Eucharist for many Christian denominations. In its most complete version, it consists of an antiphon, psalm verse and Gloria Patri, which are spoken or sung at the beginning of the celebration. It is part of the proper of the liturgy: that is, the part that changes over the liturgical year.

In the Roman Rite of the Catholic Church it is known as the antiphona ad introitum (Entrance antiphon), as in the text for each day's Mass, or as the cantus ad introitum (Entrance chant) as in the General Instruction of the Roman Missal, 47 and the First Roman Ordo (sixth to seventh century). In pre-1970 editions of the Roman Missal, the word Introitus was used, distinguished from the normal meaning of the word (entrance) by being capitalized. In Ambrosian chant and Beneventan chant, the counterpart of the Introit is called the ingressa. In the Mozarabic, Carthusian, Dominican, and Carmelite Rites, it is called the "officium".