The International Standard Musical Work Code is a unique identifier for musical works (composition and lyrical content).
An ISWC begins with the letter "T", followed by a unique nine-digit number (from 00000001 to 999999999) with an additional check digit at the end. (Written format: T-345246800-1).
Where to get one?
ISWCs are assigned by most collection societies when your songs are registered. You can also get one by visiting the International ISWC Agency.
An ISWC is not mandatory to submit your music.