This document defines the principles and specifies the requirements and guidelines for unique product identifiers, unique economic operator identifiers, and unique facility identifiers used in digital product passports. It covers the following areas: a) global uniqueness; b) persistence; c) syntax; d) semantics; e) interoperability; f) openness. This document accommodates unique product identifiers at three granularity levels of specificity:model, batch, or individual item, to support various operational needs. This document describes identification (ID) schemes that use issuing agencies, self-issuing systems, or a combination of both.