ISWC

An ISWC identifies a composition, independently of any recording of it. Where an ISRC points at one recorded performance, an ISWC points at the song: one work, one code, however many times it is recorded, covered, remixed or sampled.

The code takes the form of a T followed by nine digits and a check digit, conventionally written as T-123.456.789-0. It is assigned once per work and does not change with ownership, title variants or new recordings.

Unlike an ISRC, an ISWC is not something a writer applies for directly. It is allocated through the international registration system when the work is registered by an authorised party — a society or a publisher submitting the work with its writers, their IPIs and the agreed shares. That means the identifier only exists once someone has actually registered the song. A song that has never been registered has no ISWC, and that absence is a reliable signal of a work that will struggle to be paid correctly.

The other common failure is duplication. If the same work is registered more than once — a slightly different title, an inconsistent writer name, a co-writer's publisher submitting separately — the systems can end up holding conflicting records, which delays distribution until the conflict is resolved. Registering once, consistently, with the same writer names and IPIs everyone else is using, prevents most of it.

The connection that matters commercially is the one between the two identifiers. Matching an ISRC to its ISWC is what lets streaming income on the composition side reach the writers of the song being streamed. Where that link is missing, income accumulates unmatched — the origin of a substantial part of what the industry calls black box.