Szamosközy István (1570–1612) was a Hungarian humanist and historian.
Szamosközy was born in Kolozsvar (present day Cluj-Napoca, Romania) to a Calvinist family. He completed his studies at Heidelberg and Padova. In 1593 he returned to Hungary and started to work in Gyulafehervar (present day Alba Iulia, Romania) for the archive of the Transylvanian court. There he started collecting materials and writing his major work on Hungarian history.
Stephen Bocskai nominated him as the official court historian.
His unfinished Hungarian history was never published but parts are extant in many manuscript copies. Bethlen Farkas saved longer parts in his Transylvanian history. He designed his work based on the example of Antonio Bonfini's Decades (Tenths). Szilagyi Sandor published Szamosközy's works in four volumes in Szamosközy törteneti maradvanyai, Budapest 1876–1880.