William Schaus (January 11, 1858 in New York City – June 20, 1942) was an American entomologist who became known for his major contribution to the knowledge and description of new species of the Neotropical Lepidoptera.
William Schaus, Jr. was son of Wilhelm, later William Schaus, Sr. (1820–1892), a German-immigrant art collector and dealer, proprietor of the Schaus Galleries in New York City, and of Margaret Connover.
He was educated initially at Exeter Academy and then in France and Germany, and was influenced early in his career by Henry Edwards, although he also studied languages, art and music. Schaus received the honorary degree of Master of Arts from the University of Wisconsin in 1921, and in 1925 that of honorary Doctor of Science from the University of Pittsburgh.
Along his life he gathered an important collection of over 200,000 specimens of Lepidoptera through travels to several countries of the world such as Mexico, Costa Rica, Guatemala, Panama, Cuba, Jamaica, Dominica, Saint Kitts, the Guianas, Colombia and Brazil, and by the purchase of the Dognin Collection  of about 26,000 specimens of tropical moths and about 5,000 specimens of butterflies from the Old World, which was donated in 1901 and 1905 to the American Museum of Natural History.
In 1919 Schaus joined the Bureau of Entomology of the United States Department of Agriculture and, in 1921, began a long association with the Smithsonian Institution as an honorary curator of insects in the United States National Museum, to which he donated his library and his collection of Lepidoptera subsequent to 1905.
The genera Schausia and Schausiana were named in his honor, as well as numerous species with the specific epithet schausi . The common names of the Schaus's Crow and Schaus' Swallowtail butterflies also refer to him.
- American Lepidoptera: illustrations of new and rare species. Part I, London: R.H. Porter, 1892. (Work digitized by Biodiversity Heritage Library at )
- Descriptions of new American butterflies 1902. Kessinger Publishing (2010 reprint)
- William Schaus Papers, 1917-1939 from the Smithsonian Institution Archives
- Obituary Carl Heinrich & Edward A. Chapin (September 1942) Science 96 (2489): 244–5
- Carl Heinrich & Edward A. Chapin (September 1942). "Obituary". Science 96 (2489): 244–5. doi:10.1126/science.96.2489.244. PMID 17770518.
- "Gives 26,000 moths". The New York Times. 1905-10-25. Retrieved 2011-01-31.
- "William Schaus Papers". Retrieved 2011-01-30.
- "USNM Lepidoptera collections". National Museum of Natural History (Smithsonian Institution). Retrieved 27 October 2011.
- "Butterflies and Moths of the World - Genera authored by Schaus". Retrieved 2011-02-01.