The design and location of double bars in Beethovens autograph scores is very different from what one might deduce from recent scholarly editions of his music, which normally disregard this feature of his notation. The study of double bars has in fact been generally neglected in musicology as a whole, yet the signs present several problems. These are particularly acute in Beethovens music, especially in works that consist of movements or sections not wholly independent of each other. A survey of a large number of his autograph scores reveals that his use of double bars is very complex but largely systematic, and has significant implications for how he envisaged the boundaries between sections of his works. These implications offer fresh clues to the most appropriate interpretation in performance at relevant points. Beethovens double bars also provide startling evidence that the Third Piano Concerto was composed mainly in 1800 rather than 1803, and that the Violin Romance Op. 50 was originally the slow movement of a concerto - most likely WoO 5.