The article presents results of an obsidian sourcing study on artifacts from Tonga and Fiji. New LA-ICPMS data on obsidian source locations on Tafahi in northern Tonga are discussed in relation to inter-island mobility during two important phases in the Central Pacific: the late-Lapita phase in Fiji-West Polynesia at 2700-2600 cal. BP and during the time of the rise of Polynesian chiefdoms at ~1000-400 cal. BP. The sourcing results indicate that two sources of obsidian were exploited during Tongan prehistory. It is suggested that different modes of interaction were responsible for obsidian movement during the early and late phases of Tongan prehistory.