Ivan Klajn (Иван Клајн, ǐʋan klâjn; 31 January 1937 – 31 March 2021) was a Serbian linguist, philologist and language historian, with primary interest in Romance languages and Serbian. He was a regular member of the Serbian Academy of Sciences and Arts, and the editor-in-chief of the Matica srpska's journal Jezik danas. Through his paternal family, which lived in Vukovar for generations, he was of Croatian-Jewish descent.
He completed the studies of the Italian language and literature at the University of Belgrade Faculty of Philology. After graduation, he started working at the same faculty, becoming a regular professor of the Italian language and the comparative grammar of Romance languages. Beside Romance Studies, his interest also lies in the language morphology, linguistic consultancy and the standardization of the modern Serbian language. His major works are the Rečnik jezičkih nedoumica ('The dictionary of linguistic dilemmas'), Tvorba reči u savremenom srpskom jezi