Outrigger boats are various watercraft featuring one or more lateral support floats known as outriggers, which are fastened to one or both sides of the main hull. They can range from small dugout canoes to large plank-built vessels. Outrigger boats can also vary in their configuration, from the ancestral double-hull configuration (catamarans), to single-outrigger vessels prevalent in the Pacific Islands and Madagascar, to the double-outrigger vessels (trimarans) prevalent in Island Southeast Asia. They are traditionally fitted with Austronesian sails, like the crab claw sails and tanja sails, but in modern times are often fitted with petrol engines.

Unlike a single-hulled vessel, an outrigger or double-hull vessel generates stability as a result of the distance between its hulls rather than due to the shape of each individual hull. As such, the hulls of outrigger or double-hull boats are typically longer, narrower and more hydrodynamically efficient than those of single-hull vessels. Compared to other types of canoes, smaller outrigger canoes can be quite fast, yet are also capable of being paddled and sailed in rougher water. This paddling technique, however, differs greatly from kayaking or rowing. The paddle, or blade, used by the paddler is single sided, with either a straight or a double-bend shaft.

These vessels were the first true ocean-going ships, and are an important part of the Austronesian heritage. They were the vessels that enabled the Austronesian expansion from Taiwan into the islands of both the Indian and Pacific Ocean from around 3000 BC. They comprise the bulk of traditional boats in Island Southeast Asia, Island Melanesia, Micronesia, Polynesia, and Madagascar. They have spread to other cultures Austronesians came into contact with, notably in Sri Lanka and southern India as well as in the coast of East Africa. In modern times, outrigger vessels are used in the sport of sailing. Catamaran and trimaran configurations are also widely used for high speed craft.