Thomas Henry Huxley (1825-1895) was an eminent Victorian-era biologist, best known as a passionate defender and popularizer of Darwin's theory of evolution. His partisanship earned him the nickname of "Darwin's Bulldog," although he did not accept the theory uncritically. In addition to his work in biology, he performed original research in zoology and paleontology. He is also remembered as the progenitor of a family of highly successful scientists and thinkers. This collection is made up of letters, primarily written by Huxley, on a variety of topics including the age of man, evolution, education, natural history, science, geology, spiritualism, and vivisection. The most voluminous correspondence is with Sir James Thomas Knowles (30 letters) and with Huxley's daughter, Ethel Huxley Collier, "Babs," (44 items). The 30 letters to Knowles appear in neither the Life and Letters, nor are they listed in Dawson's guide to the Huxley Papers at the Imperial College. The other major correspondents include Charles Edward C. Appleton, Matthew Arnold, William B. Carpenter, Sir Henry Cole, George Dixon, Sir John Donnelly, Thomas Campbell Eyton, Sir William Henry Flower, Sir Joseph Dalton Hooker, Leonard Huxley, Sir William Jenner, Sir Charles Lyell, Louis Compton Miall, Alphonse Milne-Edwards, Sir James Paget, Harry Quilter, Harry Govier Seeley, Alfred R. Wallace, and William Crawford Williamson.

There is correspondence concerning geology, botany, natural history, natural selection, evolution, British science and scientists, and other scientific topics. Most of the letters are written by Lyell, with a very few items by others.