Adam Fastnacht (27 July 1913, Sanok - 16 February 1987, Wrocław) doctor hab., historian, editor. He was a distinguished Polish historian, researcher of the history of the town and the district of Sanok Land, one of the most renowned Polish historians of his time. Fastnacht was born to a German family who settled in the east. He studied in Sanok, in Lwów at Lviv University under Franciszek Bujak and at the Jagiellonian University in Kraków, where in 1946 he received his PhD. Fastnacht was a member of the Armia Krajowa.

He was long-standing curator of the Ossolineum.