Alexei Kondratiev (February 15, 1949–May 28, 2010) was an American author, linguist, and teacher of Celtic languages, folklore and culture. He taught the Irish language and Celtic history at the Irish Arts Center in Manhattan, New York from 1985 until his death on May 28, 2010. Nine editions of his book, The Apple Branch, were published in English and Spanish between 1998 and 2004. At various times, he taught all six of the living Celtic languages.