An altar server is a lay assistant to a member of the clergy during a Christian liturgy. An altar server attends to supporting tasks at the altar such as fetching and carrying, ringing the altar bell, helps bring up the gifts, brings up the book, among other things. If young, the server is commonly called an altar boy or altar girl.

The ministry of altar server in the Catholic Church is very unique, other than the priest and deacons; no one else has the opportunity to participate so closely in the preparation of the Eucharist.

The primary focus of the altar server is to assist the Priest Celebrant during the Mass. This assistance by the Altar Servers allows the congregation to concentrate and participate better in the music, the prayers, the proclamation of Scripture, and most especially, the beautiful Liturgy of the Eucharist.