In Eastern Christianity an iconostasis (the plural is iconostases, whose last syllable rhymes with ease) is a wall of icons, religious paintings, separating the nave from the sanctuary in a church. Iconostasis also refers to a portable icon stand that can be placed anywhere within a church. The modern iconostasis evolved from the Byzantine templon in the fifteenth century.

In these settings, the nave is the main space where most of the worshippers stand, and the sanctuary is the area around the altar, east of the nave. The iconostasis typically has three openings or sets of doors; the Beautiful Gates in the center, and the North and South Doors at or near either end of the iconostasis. The Beautiful Gates are sometimes called the Royal Doors, but that name more properly belongs to the central doors connecting the narthex, or porch, and the nave. The North and South Doors are often called "deacon's doors" because the deacons use them frequently; often, icons of sainted deacons are depicted on these doors (particularly St. Stephen Protomartyr and St. Ephrem the Syrian). Alternatively, Angel’s doors is also an appropriate term since the Archangels Michael and Gabriel are often depicted there.

A number of guidelines or rubrics govern which icons are on which parts of the iconostasis, although there is some room for variation. There are also guidelines for who should enter or leave the sanctuary by which door. These guidelines were developed over the course of many centuries, with both theologically symbolic and practical reasons for them.