What is OPC UA is a very simple question. The answer when you are discussing a complex technology architecture like OPC UA isn't as simple. OPC UA which I will refer to as UA throughout this book is the next generation of OPC technology. UA is a more secure, open, reliable mechanism for transferring information between Servers and Clients. It provides more open transports, better security and a more complete information model than OPC which I will refer to as OPC Classic. UA provides a very flexible and adaptable mechanism for moving data between Enterprise type systems and the kinds of controls, monitoring devices and sensors that interact with real world data.