Stanisław Kętrzyński (Polish pronunciation: [staˈɲiswaf kɛnˈtʂɨɲskʲi]; 10 September 1878 in Lwów, Austro-Hungary – 26 May 1950 in Warsaw, Poland) was a Polish historian, diplomat and freemason. He was the son of Polish historian Wojciech Kętrzyński. During the Second World War Stanisław Kętrzyński was a prisoner in the German Auschwitz concentration camp. Among his students were Stanisław Arnold, Aleksander Gieysztor, Jadwiga Karwasińska and Adam Wolff.