Reginald Aldworth Daly (March 18, 1871 – September 19, 1957) was a Canadian geologist. He was a professor at Harvard University from 1912 until 1942, after working as a field geologist for the Canadian International Boundary Commission.

He examined the rocks along a 400 miles stretch at the 49th parallel, which led him to formulate a theory of the origins of igneous rocks. He published his seminal work Igneous Rocks and Their Origin in 1914.

A crater on Mars was named in his honor.