OPC Unified Architecture (OPC UA) is a cross-platform, open-source, IEC62541 standard for data exchange from sensors to cloud applications developed by the OPC Foundation. Distinguishing characteristics are:

Although developed by the same organization, OPC UA differs significantly from its predecessor, Open Platform Communications (OPC). The Foundation's goal for OPC UA was to provide a path forward from the original OPC communications model (namely the Microsoft Windows-only process exchange COM/DCOM) that would better meet the emerging needs of industrial automation.

After more than three years of specification work and another year for a prototype implementation, the first version of the Unified Architecture was released in 2006.

The current version of the specification is on 1.04 (22 November 2017). The new version of OPC UA now has added publish/subscribe in addition to the client/server communications infrastructure.

Although the original binding to COM/DCOM helped OPC to distribute well, it had several drawbacks:

These drawbacks along with a number of other considerations pushed the decision to develop a new and independent stack for OPC UA, which replaces COM/DCOM. The main characteristics of this communication stack were:

This communication stack reflects the beginning of various innovations. The OPC UA architecture is a service-oriented architecture (SOA) and is based on different logical levels.

OPC Base Services are abstract method descriptions, which are protocol independent and provide the basis for OPC UA functionality. The transport layer puts these methods into a protocol, which means it serializes/deserializes the data and transmits it over the network. Two protocols are specified for this purpose. One is a binary TCP protocol, optimized for high performance and the second is Web service-oriented.