Pyotr Leonidovich Kapitsa (Russian Пётр Леони́дович Капи́ца) (8 July [O.S. 26 June] 1894 – 8 April 1984) was a leading Soviet physicist and Nobel Prize in Physics laureate.

Kapitsa was born in Kronstadt, Russian Empire to Leonid Petrovich Kapitsa, a military engineer who constructed fortifications, and Olga Ieronimovna Kapitsa. Kapitsa' studies were interrupted by the First World War, in which he served as an ambulance driver for two years on the Polish front. He graduated from the Petrograd Polytechnical Institute in 1918. He subsequently studied in Britain, working for over ten years with Ernest Rutherford in the Cavendish Laboratory in Cambridge. He was made a Fellow of the Royal Society in 1929 and was the first director (1930–34) of the Mond Laboratory in Cambridge. In the 1920s he originated techniques for creating ultrastrong magnetic fields by injecting high current for brief periods into specially constructed air-core electromagnets. In 1928 he discovered the linear dependence of resistivity on magnetic field for various metals in very strong magnetic fields.