A sacristy is a room for keeping vestments (such as the cassock and chasuble) and other church furnishings, sacred vessels and church treasures . The sacristy is usually located inside the church (for example, near one of the side altars or more usually behind or to the side of the main altar) but it could be an annex or separate building (as in some monasteries).

A person in charge of sacristy is called sacristan.

The sacristy is also where the priest and attendants dress and prepare before the service. They will return there at the end of the service to remove the special robes and put away any of the vessels used in the service.

Sacristies usually contain a special wash basin in which the outlet flows directly into the ground.This wash basin is used to wash remnants of Holy Communion off the ciborium, and sometimes remnants of wine from the chalice and cruets.The cruets,chalice,ciborium,paten and altar linens ; and sometimes theEucharist itself is kept inside the sacristy.

The word "sacristy" derives from the Latin "sacrastia".