Walther Wilhelm Georg Bothe (German: [ˈvaltɐ ˈboːtə] ⓘ; 8 January 1891 – 8 February 1957) was a German physicist who shared the 1954 Nobel Prize in Physics with Max Born "for the coincidence method and his discoveries made therewith".
He served in the military during World War I from 1914, and he was a prisoner of war of the Russians, returning to Germany in 1920. Upon his return to the laboratory, he developed and applied coincidence circuits to the study of nuclear reactions, such as the Compton effect, cosmic rays, and the wave–particle duality of radiation.
In 1930, he became a full professor and director of the physics department at the University of Giessen. In 1932, he became director of the Physical and Radiological Institute at the University of Heidelberg. He was driven out of this position by elements of the deutsche Physik movement. To preclude his emigration from Germany, he was appointed director of the Physics Institute of the Kaiser Wilhelm Institute for Medical Research (KWImF) in Heidelberg. There, he built the first operational cyclotron in Germany. Furthermore, he became a principal in the German nuclear energy project, also known as the Uranverein (Uranium Club), which was started in 1939 under the supervision of the Army Ordnance Office.
In 1946, in addition to his directorship of the Physics Institute at the KWImf, he was reinstated as a professor at the University of Heidelberg. From 1956 to 1957, he was a member of the Nuclear Physics Working Group in Germany.
In the year after Bothe's death, his Physics Institute at the KWImF was elevated to the status of a new institute under the Max Planck Society and it then became the Max Planck Institute for Nuclear Physics. Its main building was later named Bothe laboratory.