William Herman Rau (January 19, 1855 – November 19, 1920) was an American photographer who was active primarily in the latter half of the 19th and early 20th centuries.

[1] His older brother, George, operated a photography studio out of the Rau house,[3] and William picked up the trade while still young.

[1] In 1874, with Bell's recommendation, Rau joined an expedition to Chatham Island in the South Pacific to photograph the Transit of Venus.

[5] The expedition spent 45 days in the desert at one point, and Rau recalled being constantly threatened, harassed, and robbed by locals.

[2] In 1886, Rau made the first of several trips to Europe, photographing sites in Belgium, Germany, Switzerland, France, and Italy.

Notable events he covered included the Spanish–American War in 1898, the Klondike Gold Rush in the late 1890s, the funeral of President William McKinley in 1901, the eruption of Mount Pelée in 1902, the funeral of Admiral William T. Sampson in 1902, the America's Cup race of 1903, the Great Baltimore Fire of February 7, 1904,[2] the inauguration of President Theodore Roosevelt in 1905, and the arrival of the RMS Olympic in New York Harbor on June 21, 1911.

Rau's panoramic subjects include Niagara Falls and Hemlock Lake, and the cities of Rochester and Buffalo in New York and Easton in Pennsylvania.

[7] In an 1884 article, Rau stated that he preferred cameras with Euryscope lenses and cherry or mahogany cases, oxalate-developed plates, and a Loring finder (for capturing moving subjects).