Polynesian outliers are a number of culturally Polynesian societies that geographically lie outside the main region of Polynesian influence, known as the Polynesian Triangle; instead, Polynesian outliers are scattered in the two other Pacific subregions: Melanesia and Micronesia. Based on archaeological and linguistic analysis, these islands are considered to have been colonized by seafaring Polynesians, mostly from the area of Tonga, Samoa and Tuvalu.
The region commonly termed "Polynesia" includes thousands of islands, most of them arranged in a rough triangle bounded by Hawaii, Easter Island, and New Zealand. Outside the Polynesian Triangle, in areas commonly designated Micronesia and Melanesia, lie about two dozen islands, most of them small and widely separated, whose inhabitants speak Polynesian languages. These islands are collectively termed the Polynesian "outliers".
Their residents generally share features found within Triangle Polynesia. Physically, Polynesians tend to have brown complexions and dark, wavy hair, and they are typically large people of muscular build.
The fact that people in all of the Polynesian outliers speak recognizably Polynesian languages implies that their ancestors fairly recently migrated from the Polynesian heartland. Yet there is much social variation. In some places, outlier populations settled in close proximity to Melanesian or Micronesian populations and seem to have been influenced by them. In other locations, outlier populations remained isolated by geography, ecology, or choice and seem more classically Polynesian.
The Federated States of Micronesia has two outlier cultures, Kapingamarangi and Nukuoro. Papua New Guinea has four : Nuguria, Nukumanu, and Takuu Vu'ula or Hula. The country with the most outlier cultures is the Solomon Islands, with seven: Anuta, Bellona, Ontong Java, Rennell, Sikaiana (the Stewart Islands), Tikopia, and Vaeakau-Taumako (the Duff Islands and Reef Islands). Vanuatu has five: Emae, Makura, Mele (Erakoro, Eratapu) stemming from Rarotonga, Aniwa and Futuna. Futuna recognizes links with Tonga. The principal outlier culture in New Caledonia is on Ouvéa in the Loyalty Islands, where the Fagauvea language is spoken.
The links of these people are multiple. 
The outlier groups in Micronesia, Papua New Guinea, and the northern Solomon Islands speak Ellicean languages (which also includes Tuvaluan), while those further to the south in the Solomons, Vanuatu, and New Caledonia speak Futunic languages (which also includes the language of Wallis and Futuna). These are two of the branches of the Samoic language family, which is sometimes called the Samoan-Outlier language family for this reason. It is a sub-branch of the Nuclear Polynesian languages. In some of these islands, the outlier population may also speak the local Melanesian or Micronesian language.
A 1983 study analyzing the DNA of 2400 people in the Solomon Islands and Vanuatu have found markers which clearly distinguish the Polynesian outlier islands of the group. Of the four Polynesian outliers considered, Anuta was the most genetically distinct, followed by Rennell and Bellona. Tikopia showed more influence from the nearby Melanesian population. All indicate traces of inter-island population movements, and even sources from Europeans, Africans, and Asians, though the latter were at a low level.
Two of the more remote Polynesian outliers have disputed legal sovereignty:
- Kapingamarangi, now governed by the Federated States of Micronesia, is also legally claimed by Spain, under the 1899 treaty that ceded the Caroline Islands;
- Sikaiana, previously known as the Stewart Islands, now de facto controlled by the Solomon Islands. Ceded to the Polynesian Kingdom of Hawaii in 1856; it was included in the Republic of Hawaii which was annexed by the United States of America. Its status as an American territorial possession is disputed by the Solomon Islands.
- Feinberg, Richard and Richard Scaglion, eds. 2012. Polynesian Outliers: The State of the Art. Ethnology Monographs, No. 21. Pittsburgh: University of Pittsburgh Press.
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- Blake, N.M.; Hawkins, B.R.; Kirk, R.L.; Bhatia, K.; Brown, P.; Garruto, R.M.; Gajdusek, D.C. (December 1983). "A population genetic study of the Banks and Torres Islands (Vanuatu) and of the Santa Cruz Islands and Polynesian Outliers (Solomon Islands)". American Journal of Physical Anthropology. 62 (4): 343–61. doi:10.1002/ajpa.1330620402. PMID 6607679.
- The U.S. Territory of Palmyra Island has a similar history.