István Kniezsa (1 December 1898, Trsztena, Austria-Hungary, now Trstená, Slovakia – 15 March 1965, Budapest, Hungary) was a Hungarian linguist and Slavist, corresponding (1939) and regular (1947) member of the Hungarian Academy of Sciences. He was one of the most significant figures in Hungarian language historical research in the 20th century, achieving significant scientific results in the study of place and personal names in the Carpathian Basin, in researching the medieval state and writing practice of the Hungarian language, as well as in the exploration of foreign words of Slavic origin.