William Douglas Simpson CBE (2 August 1896 – 9 October 1968) was a Scottish academic and writer who focused on the study of medieval architecture and archaeology.

Although his archaeological findings have been superseded, his detailed studies of buildings and structures remain key documents.

He wrote numerous books and articles based on this and other research, through which he became well known as an authority on the castellated architecture of Scotland and Scandinavia.

W. Douglas Simpson was the author of a wide range of publications on architectural matters, from academic papers to general guides aimed at the tourist.

His lectures and talks were hugely successful and well attended not just by students but a more general audience.