(from Latin oriens, orientum, “the rising sun”), in architecture, the position of a building in relation to an east-west axis. In Mesopotamia and Egypt, as well as in pre-Columbian Central America, the important features of the buildings, such as entrances and passages, faced east, in the direction of the rising sun. Orientation, however, varies according to religious and practical considerations. Muslims, in their prayers, turn toward Mecca, whatever direction that may be. Accordingly, mosques are oriented so that the mihrab, or prayer niche, faces Mecca. Christian churches have usually been oriented with the apse or high altar placed at the east end, but this orientation was not always favoured. In early Christian churches, architects commonly oriented churches to the west, such as in the basilica of Old St. Peter's in Rome.

Orientation is frequently planned to take maximum advantage of the daily and seasonal variations of the sun's radiation. Optimum orientation of a structure is, in the end, a compromise between its function, its location, and the prevailing environmental factors of heat, light, humidity, and wind.