ISWC (International Standard Musical Work Code) is the unique 10-character global identifier for a musical work — i.e., the underlying composition, not a specific recording. It is the publishing-side equivalent of ISRC. Format: T-1234567890-1 (T-prefix + 10 digits + check digit).

A single composition has one ISWC regardless of how many recordings of it exist. Each recording has its own ISRC, but they all share the song's one ISWC.

ISWCs are assigned by your PRO when you register a work. Without an ISWC, royalty matching across CMOs (especially internationally) becomes unreliable — many "unmatched" royalty issues at The MLC and foreign societies trace back to missing or wrong ISWCs.

Best practice: ensure every work registered with your PRO has an ISWC, and include the ISWC in every CWR registration sent to foreign CMOs.