Abstract The Etive Dyke Swarm is the largest Caledonian dyke swarm in Britain and Ireland. Field and petrophysical (AMS–anisotropy of magnetic susceptibility) data are presented that indicate the dykes resulted from passive upwelling of magmas into fractures created by regional tectonic stresses. During the period of dyke intrusion (around 415 Ma) periodic episodes of sinistral transpression affected the region and were probably associated with sinistral movement on the Great Glen and other regional faults that lie subparallel (approximately 5° clockwise) from the long axis of the swarm. AMS data show that magma upwelled subvertically across the swarm and suggests that the dykes fed a volcanic field much larger than the now preserved Glencoe Volcano complex.