“Polynesian outliers” are not anymore considered, by many scholars of South Pacific history and anthropology, as a valid analytical category. Peoples from the islands of Futuna, Aniwa and Tanna in the South of Vanuatu share many common cultural traits. Their differences have continued to fade since initial Polynesian contacts with Tanna and have been further weakened through Christianization and colonisation. Nevertheless, the historical landing on these islands of Aniwa and Futuna by settlers coming from Central Polynesia deeply influenced the whole socius of Tanna, their closest and larger neighbour island. Cultural, social, political, economical, religious and linguistic influences have transfigured ancient Tannese society. This paper provides a summary of evidence that clearly illustrates the syncretistic processes that gave birth to pre-colonial Tannese tradition. This syncretistic process can be seen as a product of an articulated expansionist strategy of in-coming migrant groups from Futuna. Explicit syncretic elements include a rich ceremonial complex as well as a transformed ceremonial hierarchy. These strong cultural interactions between the “Polynesian” and “Melanesian” on Tanna have engendered much local experience with cultural adaptation to drastic social changes. This experience shaped the ways in which islanders later adapted to Christianisation and to colonial domination, while simultaneously contesting the new imported order with inventive indigenous politico-religious movements.