An ISWC (International Standard Work Code) is a unique, permanent and internationally recognized reference number for the identification of compositions (musical works). It begins with the letter "T" and is followed by a unique 9-digit number with an additional check digit at the end (i.e. T-345246800-1).

The ISWC enables the use of standard codes and data to make the administration of rights, usage identification and distribution of royalties more efficient on a worldwide basis. It is a key component used by rights organizations to match performances and pay royalties. It was originally designed for the benefit of the key music publishing value chain participants: songwriters, composers, authors, lyricists, producers, publishers, broadcasters, tracking services and PRO members of CISAC.

Other codes exist for similar purposes, such as the ISRC (International Standard Recording Code) for sound recordings.