Every commercially released recording gets an ISRC, and it stays with that recording for good. Play it on radio, sell it as a download, stream it or licence it into a film, and the same code comes back in the reporting.
What it looks like
Twelve characters, for example NLA321500001: a two-letter country code, a three-character registrant code, two digits for the year, and a five-digit number the registrant assigns.
One per recording
A new code is needed for every distinct recording, which includes a radio edit, a remix, a live version and a re-recording of the same song. A new master of the same recording keeps its code. It is separate from the ISWC, which identifies the composition rather than the recording.
Where the codes come from
A national ISRC agency issues a registrant code to a label or a self-releasing artist. Most distributors assign codes automatically when you supply none, which works until you change distributor and want the catalogue to stay consistent.
Why it matters
Airplay monitoring, streaming reports and neighbouring rights all match on ISRC. A missing or duplicated code means plays nobody can attribute.