The Sama-Bajau refers to several Austronesian ethnic groups of Maritime Southeast Asia with their origins from the southern Philippines. The name collectively refers to related people who usually call themselves the Sama or Samah; or are known by the exonyms Bajau (also spelled Badjao, Bajaw, Badjau, Badjaw, Bajo or Bayao) and Samal or Siyamal (the latter being considered offensive). They usually live a seaborne lifestyle, and use small wooden sailing vessels such as the perahu (layag in Meranau), djenging, balutu, lepa, pilang, and vinta (or lepa-lepa).
The Sama-Bajau are traditionally from the many islands of the Sulu Archipelago in the Philippines, coastal areas of Mindanao, northern and eastern Borneo, the Celebes, and throughout eastern Indonesian islands. In the Philippines, they are grouped together with the religiously-similar Moro people. Within the last 50 years, many of the Filipino Sama-Bajau have migrated to neighbouring Malaysia and the northern islands of the Philippines, due to the conflict in Mindanao. As of 2010, they were the second-largest ethnic group in the Malaysian state of Sabah.
Sama-Bajau have sometimes been called the "Sea Gypsies" or "Sea Nomads", terms that have also been used for non-related ethnic groups with similar traditional lifestyles, such as the Moken of the Burmese-Thai Mergui Archipelago and the Orang Laut of southeastern Sumatra and the Riau Islands of Indonesia. The modern outward spread of the Sama-Bajau from older inhabited areas seems to have been associated with the development of sea trade in sea cucumber (trepang).
Sama-Bajau are noted for their exceptional abilities in free-diving. Divers work long days with the greatest daily apnea diving time reported in humans of greater than 5 hours per day submerged. Some Bajau intentionally rupture their eardrums at an early age to facilitate diving and hunting at sea. Many older Sama-Bajau are therefore hard of hearing.
More than a thousand years of subsistence freediving associated with their life on the sea appear to have endowed the Bajau with several genetic adaptations to facilitate their lifestyle. A 2018 study showed that Bajau spleens are about 50% larger than those of a neighboring land-based group, the Saluan, letting them store more haemoglobin-rich blood, which is expelled into the bloodstream when the spleen contracts at depth, allowing breath-holding dives of longer duration. This difference is apparently related to a variant of the PDE10A gene. Other genes that appear to have been under selection in the Bajau include BDKRB2, which is related to peripheral vasoconstriction, involved in the diving response; FAM178B, a regulator of carbonic anhydrase, which is related to maintaining blood pH when carbon dioxide accumulates; and another one involved in the response to hypoxia. These adaptations most likely result from an increased frequency of alleles widely distributed in human populations. Members of another "sea gypsy" group, the Moken, have been found to have better underwater vision than Europeans, although it is not known if this trait has a genetic basis.