Duncan MacLaren Young Sommerville FRSE FRAS (1879–1934) was a Scottish mathematician and astronomer.

The middle name 'MacLaren' is spelt using the old orthography M'Laren in some sources, for example the records of the Royal Society of Edinburgh.

In 1905 he gained his doctorate (DSc) for his thesis, Networks of the Plane in Absolute Geometry and was promoted to lecturer.

In 1911 Sommerville published his compiled bibliography of works on non-euclidean geometry, and it received favorable reviews.

His proposers were Peter Redford Scott Lang, Robert Alexander Robertson, William Peddie and George Chrystal.

In 1915 Sommerville went to New Zealand to take up the Chair of Pure and Applied Mathematics at the Victoria College of Wellington.

When his Introduction to Geometry of N Dimensions appeared in 1929, it received a positive review from B. C. Wong in the American Mathematical Monthly.