The results of obsidian sourcing studies from the Anir Island assemblages are presented and compared with other studies to develop a regional picture of obsidian distribution and use over a three and a half thousand year period for the Bismarck Archipelago, Papua New Guinea. Predicted changes in technology and mobility patterns are correlated with regional changes in the frequency and distribution of obsidian from particular sources in the region. Early Lapita assemblages in most parts of the archipelago were dominated by west New Britain obsidian. In the Middle Lapita period changes occurred in the northern and eastern Bismarck Archipelago and assemblages here became dominated by Admiralty Islands obsidian. In later periods, west New Britain obsidian re-gained dominance in some areas. Nevertheless, in the Lapita phases pottery assemblages suggest exchange was between culturally similar, socially related groups.