The offertory (from Medieval Latin offertorium and Late Latin offerre) is the part of a Eucharistic service when the bread and wine for use in the service are ceremonially placed on the altar.
A collection of alms from the congregation, such as may take place also at non-Eucharistic services, often coincides with this ceremony.
The Eucharistic theology may vary among those Christian denominations that have a liturgical offertory.
In the Roman Rite, the term "preparation of the gifts" is used in addition to the term "offertory".
In the Roman Rite, the offertory is the first part of the Liturgy of the Eucharist. The altar is first prepared by placing on it the corporal, purificator, missal and chalice. The bread and wine, and perhaps other offerings or gifts for the poor or for the Church, are presented by the faithful in a procession to the accompaniment of an offertory chant. The priest places first the bread and then the wine on the altar while saying the prescribed prayers, after which he may incense them together with the cross and the altar. The priest and the people may also be incensed. After washing his hands at the side of the altar, the priest says the Prayer over the Offerings. This was originally the only prayer said at the offertory of the Roman Rite.
There are variations in other rites. For instance, in the Dominican Rite a single prayer is said at the offertory over the bread and wine, which were already been prepared on the altar at an earlier part of the Mass.
In the Byzantine Rite, there is a short offertory at the same point as in the Roman Rite. A more elaborate ceremonial, the Liturgy of Preparation, takes place before the public part of the celebration of the Divine Liturgy.