This specification defines the UUIDs (Universally Unique IDentifiers) and the UUID Uniform Resource Name (URN) namespace. UUIDs are also known as GUIDs (Globally Unique IDentifiers). A UUID is 128 bits long and is intended to guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System and later in the Open Software Foundation's (OSF) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms. This specification is derived from the DCE specification with the kind permission of the OSF (now known as The Open Group). Information from earlier versions of the DCE specification have been incorporated into this document. This document obsoletes RFC4122.

This specification defines the UUIDs (Universally Unique IDentifiers) and the UUID Uniform Resource Name (URN) namespace. UUIDs are also known as GUIDs (Globally Unique IDentifiers). A UUID is 128 bits long and is intended to guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System and later in the Open Software Foundation’s (OSF) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms.