IEC 63339:2024 specifies the unified reference model for smart manufacturing (URMSM) using a terminology and structure, and establishes criteria for creating reference models, as specializations, that support smart manufacturing. The terminology and structure comprise a set of common modelling elements, their associations, and conformance criteria. These common modelling elements address aspects and perspectives of products and production and their lifecycle considerations. The URMSM enables an approach for creating multiple models based upon a reference model that is sufficient for understanding significant relationships among entities involved in smart manufacturing (SM) and for the development of standards and other specifications. The URMSM specifications in this document accommodate consistent, coherent, compatible specializations for relevant aspects of manufacturing systems consisting of equipment, products, and services within the domain of manufacturing. Provisions of this document are applicable for a new smart manufacturing reference model (SMRM) or elaboration of existing SMRM capabilities, for example, improving capabilities for analysis of opportunities and synthesis of technological advances, and improving interoperability of new and existing systems. This document is not intended to prescribe interoperability considerations or data schemas of models. Standardization of content relative to models will be the subject of other standards and texts specific to those model domains.