Proto Oceanic (POc) is the immediate ancestor of the Oceanic subgroup of the Austronesian language family. This subgroup consists of all 400 or so Austronesian languages of Melanesia east of 136°E, together with the languages of Polynesia and (with two exceptions) those of Micronesia—more than 450 languages in all  (see map). Systematic arguments for the existence of Oceanic as a clearly demarcated branch of Austronesian were first put forward by Otto Dempwolff in the 1920s and 30s, who (under the label Urmelanesisch) made the first reconstructions of Proto Oceanic phonology and lexicon (Dempwolff 1937). The validity of the subgroup is now recognised by virtually all scholars working in Austronesian historical linguistics.
The development and break-up of the POc language and speech community were stages in a truly remarkable chapter in human prehistory. The colonisation by Austronesian speakers of the Indo-Pacific region began in the period after about 3000 BC. The outcome was the largest of the world's well-established language families and (until the expansion of Indo-European after Columbus) the most widespread. The Austronesian family comprises more than 1,000 distinct languages. Its eastern and western outliers, Madagascar and Easter Island, are two-thirds of a world apart, and its northernmost extensions, Hawaii and Taiwan, are separated by 70 degrees of latitude from its southernmost outpost, Stewart Island in New Zealand. 
It is likely that the divergence of Oceanic from its nearest relatives, which are the Austronesian languages spoken around Cenderawasih Bay and in South Halmahera (Blust 1978), began when Austronesian speakers from the Cenderawasih Bay area moved eastwards along the north coast of New Guinea and into the Bismarck Archipelago in northwest Melanesia. The area of greatest genetic diversity within Oceanic and the most likely primary dispersal centre is the Bismarck Archipelago. There is a strong school of opinion that associates the subsequent break-up of POc with the rapid colonisation of Island Melanesia and the central Pacific by bearers of the Lapita culture (see map) between about 1500 and 1000 BC. 
Beginning in the 2nd millenium BC, speakers of the Oceanic branch of Austronesian spread from northwest Melanesia into previously uninhabited regions of southern Melanesia and on into the central Pacific, leaving today some 450 languages as the linguistic remnants. The initial stages of this remarkable linguistic diaspora left well-defined archaeological footprints, which allow the directions of the expansion to be to be traced and dated rather precisely. In the middle of the 2nd millennium BC a distinctive culture appeared suddenly in north-west Melanesia in the Bismarck Archipelago, the arc of islands extending from New Britain to the Admiralties. This culture, known as Lapita, was quite different from anything that preceded it in the archeological record of Melanesia, being characterised by quite large permanent settlements on coastal beach terraces, with extensive manufacture of pottery, including a variety of vessel shapes, some decorated by finely-executed motifs stamped into the clay (Green 1991, Kirch 1997, 2001, Spriggs 1997). In the space of just three or four centuries, between about 1300 and 900 BC, the Lapita culture spread from the Bismarck Archipelago as far as Tonga and Samoa, some 6000 km to the east. 
These events were the most spectacular phase of a larger event: the Austronesian diaspora. Between about 3000 and 1000 BC speakers of Austronesian languages spread across Island South-East Asia—almost certainly beginning in Taiwan—into the western fringes of Micronesia (the Marianas and Belau) and into Melanesia. Much later they began trading expeditions to India and East Africa. The east-west boundaries of the Austronesian language family (Madagascar and Easter Island) are two-thirds of a world apart and the northernmost extensions (Hawai'i and Taiwan) are separated by 70 degrees of latitude from the southernmost outpost (Stewart Island, New Zealand). With about one thousand distinct languages Austronesian is (with Niger-Congo) the most numerous of the world‘s language families.
The history of the Austronesian language family has been the subject of research and debate for over a century, much intensified over the past 40 years. Especially in the last two or three decades, this linguistic research been joined to research by archaeologists, ethnologists, geneticists and biological anthropologists on the origins and spread of particular elements and systems of culture, genes and skeletal morphology (Bellwood, Fox and Tryon 1995, Blust 1995, Irwin 1992, Kirch 1997, 2001, Pawley 2002, Pawley and Ross 1993, Spriggs 1997, Terrell 1986 are overviews of multi-disciplinary research.) It has become evident that the mechanisms enabling Austronesian-speaking peoples to spread so rapidly, and to successfully colonise new lands, including many already inhabited, were an efficient sailing technology, and an economy based on agriculture and aboriculture and a diversity of fishing techniques.
In the Philippines and the Indo-Malaysian archipelago distances between islands are modest and the larger islands have rich land faunas and floras to exploit. It was speakers of Oceanic languages who were the world's first true ocean-going sailors, able to make deliberate voyages, carrying domesticated animals and plants, across ocean gaps of hundreds, even thousands of kilometres. They were able to glean a living on small islands with impoverished flora and land fauna. 

Bellwood, Peter S. and James J. Fox and Darrell Tryon (eds), 1995. The Austronesians: historical and comparative perspectives. Canberra: Department of Anthropology, Research School of Pacific and Asian Studies, The Australian National University.

Blust, Robert A., 1978. Eastern Malayo-Polynesian: a subgrouping argument. In S.A. Wurm and Lois Carrington (eds), Second International Conference on Austronesian Linguistics: proceedings, 181–234. Pacific Linguistics C-61. Canberra: Pacific Linguistics.

Blust, Robert A., 1995. The prehistory of the Austronesian-speaking peoples: a view from language. Journal of World Prehistory 9:453--510.

Dempwolff, Otto, 1938. Vergleichende Lautlehre des Austronesischen Wortschatzes. 2: Deduktive Anwendung des Urindonesischen auf austronesische Einzelsprachen. Beihefte zur Zeitschrift für Eingeborenen-Sprachen 19. Berlin: Dietrich Reimer.

Green, Roger C., 1991. A reappraisal of the dating from some Lapita sites in the Reef/Santa Cruz Group of the Southeast Solomon Islands. Journal of the Polynesian Society 100:197–207.

Irwin, Geoffrey, 1992. The prehistoric exploration and colonization of the Pacific. Cambridge: Cambridge University Press.

Kirch, Patrick V., 1997. The Lapita peoples: Ancestors of the Oceanic world. Oxford: Blackwell.

Kirch, Patrick V. and Roger C. Green, 2001. Hawaiki, ancestral Polynesia: An essay in historical anthropology. Cambridge: Cambridge University Press.

Pawley, Andrew, 2002. The Austronesian dispersal: Languages, technologies and people. In Peter Bellwood  and Colin Renfrew (eds), Examining the farming/language dispersal hypothesis. Cambridge: MacDonald Institute for Archaeological Research, University of Cambridge.

Pawley, Andrew and Malcolm Ross, 1993. Austronesian historical linguistics and culture history. Annual Review of Anthropology 22:425–459.

Spriggs, Matthew J.T., 1997. The Island Melanesians. Oxford: Blackwell.

Terrell, John, 1986. Prehistory in the Pacific islands. Cambridge: Cambridge University Press.