Thomas Nelson Annandale CIE FRSE (15 June 1876 in Edinburgh – 10 April 1924 in Calcutta) was a Scottish zoologist, entomologist, anthropologist, and herpetologist.
The eldest son of Thomas Annandale, the regius professor of clinical surgery at the University of Edinburgh, Nelson was educated at Rugby School, Balliol College, Oxford, and the University of Edinburgh.
Annandale went to India in 1904 as Deputy Superintendent of the Natural History Section of the Indian Museum. He was a deputy director at the Indian Museum in Calcutta and in 1907 he became its director, succeeding John Anderson (1833–1900). He had travelled widely before his career in India and with H. C. Robinson he had undertaken the Skeat Expedition to the northern part of the Malay Peninsula in 1899.
He started the Records and Memoirs of the Indian Museum journals and in 1916, he became the first director of the Zoological Survey of India that he helped found. He was associated with many scientists of his time. This change placed an official equality with botany and geology and made more funds available for expeditions to various parts of India. He was interested in aspects beyond systematics including ecology. His suggestion of a problem in anthropology to P. C. Mahalanobis led to the latters discovery of a technique that developed into the multivariate statistical techniques of today. He held the position of director until 1924 and was succeeded by Robert Beresford Seymour Sewell (1880–1964). He was president of the 1924 session of the Indian Science Congress.