ISWC (International Standard Musical Work Code)
A unique identifier for a musical composition, distinct from any particular recording of it.
What it means
The International Standard Musical Work Code (ISWC) is a unique reference number assigned to a musical composition or work. While the ISRC identifies a specific sound recording, the ISWC identifies the underlying composition — the melody, harmony, and lyrics that exist independently of any particular recorded performance. This distinction is important because a single composition can have many different recordings (covers, remixes, orchestral arrangements), and each of those recordings will have its own ISRC, but they all share the same underlying composition identified by the ISWC. ISWCs are assigned by authorized agencies, typically the national PROs or their affiliates, working under the authority of CISAC (the International Confederation of Societies of Authors and Composers). When you register a composition with your PRO, an ISWC is eventually assigned to that work. The ISWC helps ensure that all performances and recordings of your composition are properly linked, so that royalties from cover versions, international performances, and various recordings all flow back to the correct composer. For ambient music creators who frequently create variations and arrangements of their themes, understanding ISWCs is essential. An ambient piece and its extended meditation version may share the same ISWC if the composition is substantially the same, even though they have different ISRCs as recordings.
Technical details
The ISWC format follows ISO 15707 and consists of a letter prefix "T" followed by 9 digits and a check digit (e.g., T-345.246.800-1). ISWCs are assigned through the ISWC system managed by CISAC, with local agencies (typically PROs) handling the registration process. The assignment typically occurs after a work is registered with a PRO and may take several months. ISWCs are linked to works in the CISAC Common Information System (CIS-Net), which facilitates international royalty tracking. Unlike ISRCs, which creators can self-assign, ISWCs are assigned by authorized agencies. A composition maintains the same ISWC regardless of how many times it is recorded, arranged, or adapted, as long as the fundamental musical work remains the same.
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