William Allan Neilson (28 March 1869 – 13 February 1946) was a Scottish-American educator, writer and lexicographer, graduated in the University of Edinburgh in 1891 and became a PhD in Harvard University in 1898.

Neilson was born in Doune, Scotland on 28 March 1869.

Neilson was author of a number of critical works on William Shakespeare, Robert Burns and the Elizabethan theatre, editor of the Cambridge and Tudor editions of Shakespeare (1906, 1911) and editor of Webster's New International Dictionary, Second Edition (1934).

[3] Less known is his translation of the famous late 14th century Middle English alliterative chivalric romance Sir Gawain and the Green Knight.

[4][5] He died at the Smith College infirmary in Northampton, Massachusetts on 13 February 1946.