Long-term environmental change in Co. Mayo, on the mid-Atlantic seaboard of Ireland, is discussed. Pollen diagrams and bog pine, dated by ¹⁴C and dendrochronology, provide evidence for woodlands, farming and climate change. Intensive farming is dated to the early Neolithic (3800–3400 BC) prior to wide-scale spread of blanket bog. Construction of the peat-covered, stone-wall field system at Céide Fields occurred at this time which is unexpectedly early. Bronze and Iron Age activity is detailed.