Alexander Keiller FSA, FGS (1 December 1889 – 29 October 1955) was a Scottish archaeologist, pioneering aerial photographer, businessman and philanthropist.

He used his wealth to acquire a total of 950 acres (3.8 km2) of land in Avebury for preservation, where he conducted excavations and re-erected some standing stones.

On 2 June 1913, Keiller married Florence Marianne Phil-Morris (1883–1955), the daughter of artist Philip Richard Morris.

Her contributions in this field include detailed illustrations of the stones as part of the West Kennet Avenue excavations and the creation of visual reconstructions of faces from skulls, four of which were from a burial mound at Chippenham.

This work led to their publication of Wessex from the Air in 1928, which Lynda Murray notes was "the first book of aerial archaeology to be published in the UK".

In 1934, he began a two-year excavation of the West Kennet Avenue, which led south east from the Avebury stone circle.

Stuart Piggott notes that Keiller "adopted a policy of imaginative but judicious conservation and restoration of the Avebury monuments, and systematically purchased land to preserve these and their surroundings".

Keiller opened his museum that year, to display finds from the Windmill Hill, West Kennet, and Avebury excavations.

Keiller joined the special constabulary at Marlborough and as his duties left little time for archaeology, he had the museum mothballed.

In 1943, Keiller sold his holdings in Avebury to the National Trust for £12,000, simply the agricultural value of the 950 acres (3.8 km2) he had accrued, and not reflecting the immense investment he had made at the site.