Using repeat-pass satellite feature tracking, the dynamic behaviour of Jakobshavn Isbr¿, which drains around 7% of the Greenland ice sheet, is investigated in improved detail through its recent period of thinning, acceleration and retreat. The departure in 1995 from the normal seasonal invariance in velocity near the grounding line suggests a possible change in dynamics well before the subsequent thinning phase. The initiation of the acceleration and retreat is pinpointed to spring 1998 and may have been prompted by the same mechanism that gave rise to the spring 1995 flow increase.