A fore-and-aft rig is a sailing ship rig with sails set mainly in the median plane of the keel, rather than perpendicular to it, as on a square-rigged vessel.

Fore-and-aft rigged sails include staysails, Bermuda rigged sails, gaff rigged sails, gunter rig, lateen sails, lug sails, tanja sails, the spanker sail on a square rig, and crab claw sails.

Fore-and-aft rigs include:

Barques and barquentines are partially square rigged and partially fore-and-aft rigged.

A rig which combines both on a foremast is known as a hermaphroditic rig.

The fore-and-aft rig is believed to have been developed independently by the Austronesian peoples some time after 1500 BC with the invention of the crab claw sail. It is suggested that it evolved from a more primitive V-shaped "square" sail with two spars that come together at the hull. Crab claw sails spread from Maritime Southeast Asia to Micronesia, Island Melanesia, Polynesia, and Madagascar via the Austronesian migrations. Austronesians in Southeast Asia also later developed other types of fore-and-aft sails, such as the tanja sail (also known as the canted square sail, canted rectangular sail, or the balance lug sail).

Their use later spread into the Indian Ocean since the first millennium, among vessels from the Middle East, South Asia, and China.

The lateen was developed in the Mediterranean as early as the 2nd century AD, during Roman times. It became common by the 5th century.