This International Standard — provides a set of datatype definitions for representing and exchanging basic concepts that are commonly encountered in healthcare environments in support of information exchange in the healthcare environment; — specifies a collection of healthcare-related datatypes suitable for use in a number of health-related information environments; — declares the semantics of these datatypes using the terminology, notations and datatypes defined in ISO/IEC 11404, thus extending the set of datatypes defined in that standard; — provides UML definitions of the same datatypes using the terminology, notation and types defined in Unified Modelling Language (UML) version 2.0; — specifies an XML (Extensible Mark-up Language) based representation of the datatypes. The requirements which underpin the scope reflect a mix of requirements gathered primarily from HL7 Version 3 and ISO/IEC 11404, and also from CEN/TS 14796, ISO 13606 (all parts) and past ISO work on healthcare datatypes. This International Standard can offer a practical and useful contribution to the internal design of health information systems, but is primarily intended to be used when defining external interfaces or messages to support communication between them.