One identifier, one permanent address.
Every record has a stable URL built from its OSID. Paste an OSID to resolve it, or cite the address directly — it will resolve for as long as the catalog exists.
ISO 3166 code for the issuing authority. Defunct entities use withdrawn ISO codes or OSC's X-prefix namespace — see the registry.
Four-digit year of first issue — the design's introduction, not the print date. Minimum is 1840.
Face value plus normalized currency code. Decimal values use a period; non-denominated stamps use spec tokens.
The Nth distinct record sharing the first three segments. Shades and varieties increment it. 0000 is invalid.
The grammar is fixed and documented in the OSID specification. An OSID never changes once assigned. If a record is found to be in error, a new canonical record is created and the old OSID is deprecated — but it still resolves, for decades, redirecting to its successor. See how to cite and the API reference for machine access.