Erwin Stein (7 November 1885 – 17 July 1958) was an Austrian musician and writer, prominent as a pupil and friend of Schoenberg, with whom he studied between 1906 and 1910. He was one of Schoenberg's principal assistants in organizing the Society for Private Musical Performances. In 1924 it was Stein to whom Schoenberg entrusted the delicate as well as important task of writing the first article – Neue Formprinzipien ('New Formal Principles') – on the gradual evolution of what was soon to be explicitly formulated as 'twelve tone technique'. Until 1938 he lived in Vienna, where he was respected as a music teacher and conductor as well as a writer active on behalf of the music and composers he valued.
After the Anschluss he fled to London to escape the Nazis and worked for many years as an editor for the music publishers Boosey & Hawkes. His focus was mainly on Mahler, Schoenberg and Britten (all three of whom he knew personally) as well as his colleagues within the Schoenberg circle, Berg and Webern.
His books include Orpheus in New Guises (a collection of writings from the period 1924–1953) and Form and Performance (1962). He was the editor of the first collection of Schoenberg's letters (Germany 1958; UK 1964). He was also instrumental in setting up the modern music periodical Tempo in 1939.
Stein married Sophie Bachmann (1883?–1965), and their daughter, the pianist Marion Stein, married successively George Lascelles, 7th Earl of Harewood and the Liberal politician Jeremy Thorpe.