Ancient DNA studies have identified western Scotland as the only known region in Britain where inter-breeding occurred between early 4th millenniumbcNeolithic migrants and the indigenous Mesolithic population. By drawing on excavations at Mesolithic and Neolithic sites on the Isle of Islay, I identify a period of population overlap and suggest three scenarios for Mesolithic–Neolithic interaction: swift succession, dual population, and biocultural merger. These scenarios are evaluated against the archaeological evidence from Islay and elsewhere in western Scotland, and with reference to patterns of Mesolithic–Neolithic interaction in continental Europe. A cautious preference is expressed for biocultural merger, occurring between the mid-4th and mid-3rd millenniabc, a period that could be termed the ‘Neomesolithic’.