Beethoven's correspondence provides an essential key to understanding his works and personality. This edition was produced by the Beethoven-Archiv and involved much detective work. It was published between 1996 and 1998 by G. Henle Publishers. Each letter is accompanied by information concerning its origin, where it is held, etc. as well as explanatory notes. The letters are published in seven volumes (Volume 7 = index). Volume 8 (documents, subject index) is in progress.