Essay
ISWC vs ISRC: What's the Difference, and Do You Need Both?
ISWC identifies a song. ISRC identifies a recording. One song can have many ISRCs but only one ISWC.
ISRCs are usually assigned by your distributor at release. ISWCs are assigned by a PRO when the composition is registered. Matching them is how a cover, a remix, and the original all pay the same writers.