An altarpiece is a picture or relief representing a religious subject and suspended in a frame behind the altar of a church. The altarpiece is often made up of two or more separate panels created using a technique known as panel painting. It is then called a diptych, triptych or polyptych for two, three, and multiple panels respectively. Groups of statuary can also be placed on the altar. Sometimes the altarpiece is set on the altar itself.

If the altar stands free in the choir, both sides of the altar-piece can be covered with painting. The screen, retable or reredos are also commonly decorated.

Famous examples are

• the Byzantine Pala d'Oro in the Basilica di San Marco, Venice
• the Ghent Altarpiece (1432) by Hubert and Jan van Eyck
• the Isenheim Altarpiece by Matthias Grünewald
• the Altar of Veit Stoss