ISWC stands for International Standard Musical Work Code. ISWCs are recognized globally as the unique standard for world-wide identification of musical works. So, just like an ISRC, an ISWC represents a unique identification number used to separate your musical work/composition from all other similar works.
Songs receive ISWC's when they are registered at a performing rights organization (PRO). If your song is brand new, Songtrust helps register it to be assigned an ISWC.
ISWC codes are used to identify information such as:
Remember that each musical work/composition can only ever have one ISWC code attached to it, and this code should never be reused to represent other musical works/compositions. Arrangements, adaptations and translations should receive their own unique ISWC's.
ISWC's are issued by your PRO, so if your works are already registered with your PRO, they have been assigned ISWCs.
An ISWC looks like this: T-123.456.789-Z and you can find them by searching for your songs in your PRO's respective repertory on their website.