An International Standard Musical Work Code (ISWC) is an 11-character alphanumeric code that uniquely identifies a musical composition.
Each song or composition should have only one ISWC, which remains the same across all platforms, publishers, and societies. However, new versions of a song (such as arrangements, adaptations, or translations) receive their own unique ISWCs.
ISWCs are assigned and managed by your Performing Rights Organization (PRO) (for example, ASCAP, BMI, or SESAC in the U.S.). If your works are already registered with your PRO, they have likely already been assigned ISWCs.