William Herman Rau was an American photographer, active primarily in the latter half of the 19th and early 20th centuries. He is best remembered for his stereo cards of sites around the world, and for his panoramic photographs of sites along the Pennsylvania Railroad. He was official photographer of the St. Louis World's Fair in 1904, and of the Lewis and Clark Centennial Exposition in Portland in 1905. His work is now included in the collections of the Smithsonian Institution and the Getty Museum.