A rib vault or ribbed vault is an architectural feature for covering a wide space, such as a church nave, composed of a framework of crossed or diagonal arched ribs. Variations were used in Roman architecture, Byzantine architecture, Islamic architecture, Romanesque architecture, and especially Gothic architecture. Thin stone panels fill the space between the ribs. This greatly reduced the weight and thus the outward thrust of the vault. The ribs transmit the load downward and outward to specific points, usually rows of columns or piers. This feature allowed architects of Gothic cathedrals to make higher and thinner walls and much larger windows.

It is a type of arcuated, or arched, vault in which the severies, or panels in the bays of the vault's underside are separated from one another by ribs which conceal the groins, or the intersections of the panels. Rib vaults are, like groin vaults, formed from two or three intersecting barrel vaults; the ribs conceal the junction of the vaults.

The earliest surviving example in Islamic architecture is at the Mosque–Cathedral of Córdoba in al-Andalus, which predates the earliest Romanesque examples by a century. An alternative to barrel vaults in the naves of churches, rib vaults in 12th century early Gothic architecture began to be used in vaults made with pointed arches, already known in the Romanesque style. In these vaults, as in groin vaults, the weight was directed it to the corners, where piers, columns, or walls could support it. Walls in Gothic buildings were often abutted by flying buttresses. These elements made it possible to construct buildings with much higher and thinner walls than before, with immense bays, and larger stained glass windows filling the structure with light.

Cross vaults are constructed of narrow, arched ribs that diagonally cross the area to be covered. The severies can be filled with small pieces of masonry, eliminating much of the massive weight of barrel vaults. These rib vaults could also more efficiently cover large rectangular areas. Thanks to the pointed arch employed in Gothic architecture, builders could raise or lower the arches so they would have the same height for a short span or a long span, something not possible with round arches. Pointed arches also made two intersecting vaults of the same height but different widths easier to construct.