IEC 62541-3:2020 defines the OPC Unified Architecture (OPC UA) AddressSpace and its Objects. This document is the OPC UA meta model on which OPC UA information models are based. This third edition cancels and replaces the second edition published in 2015. This edition includes the following significant technical changes with respect to the previous edition: a) Added new improved approach for exposing structure definitions. An Attribute on the DataType Node now simply contains a binary description. b) Added new flags for Variables to indicate atomicity when reading or writing. c) Added Roles and Permissions to allow configuration of a role-based authorization. d) Added new data types: “Union”, “ Decimal”, “OptionSet”, “DateString”, “TimeString”, “DurationString”, NormalizedString”, “DecimalString”, and “AudioDataType”. e) Added definition on how to use the ModellingRules OptionalPlaceHolder and MandatoryPlaceHolder for Methods. f) Added optional Properties “ MaxCharacters” and “MaxByteStringLength” to Variable Nodes.