Ivan Klajn (Serbian Cyrillic: Иван Клајн, pronounced [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. In 2017, he signed the Declaration on the Common Language of the Croats, Serbs, Bosniaks and Montenegrins.