Ethernet is now taking over as the preferred communication technology in industrial automation. Fieldbuses and proprietary solutions are rapidly being replaced by Ethernet based solutions with superior performance, robustness, flexibility and functionality. This transition means that automation systems are turning into complex communication networks. The main benefits of going for Ethernet  for the manufacturers and end users are the wide availability of software, hardware and various tools, the attractive price/performance ratio and a vast potential for replacing costly manual intervention with smart network behaviour throughout the lifecycle of a system. This chapter will look at some key aspects of Ethernet as an automation network.