This palaeoglaciological reconstruction, based on the distribution of glacial lineations interpreted from satellite imagery, considers the extent, thickness and dynamics of the Welsh Ice Cap and its interaction with the British–Irish Ice Sheet. Two major ice-flow events were identified. The oldest phase of ice flow (Event I) is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north–central Wales and by ice thick enough to cover the mountain summits. At this time the interior of the ice cap is inferred to have been dominated by cold-based ice. During the growth of the Welsh Ice Cap it became confluent with the British–Irish Ice Sheet. The Welsh Ice Cap at this time was again sufficiently thick to submerge the highest mountain summits. The youngest detected phase of ice flow (Event II) was marked by an abrupt change in the dynamics of the Welsh Ice Cap. During Event II the Welsh Ice Cap was drained by at least four ice streams, which followed major troughs in northern and eastern Wales.