The OPC UA (OPC Unified Architecture) protocol is a platform-independent, service-oriented, and secure communication framework designed for industrial automation and data exchange. It enables interoperability across devices, systems, and applications from different vendors by defining standardized data models and communication methods. OPC UA integrates functionalities of the older OPC Classic specifications (data access, alarms/events, historical data) while enhancing platform independence (working on any OS from embedded devices to cloud), and improving security with encryption, authentication, and auditing. OPC UA supports two communication models: client-server (request/response) and publish-subscribe (for pushing notifications). It can use various transport protocols including TCP, UDP, WebSockets, MQTT, and AMQP, with the most common being TCP for secure, efficient data transport. Security features include message signing, session encryption, user authentication via certificates or credentials, and access controls. OPC UA's extensible architecture allows adding new technologies without impacting existing applications, making it future-proof. This protocol is widely used for real-time data acquisition, process control, and digital transformation across industrial sectors, supporting Industry 4.0 and IoT initiatives by providing secure, reliable, and standardized communication.