IEC 62270:2013 addresses the application, design concepts, and implementation of computer-based control systems for hydroelectric plant automation. It addresses functional capabilities, performance requirements, interface requirements, hardware considerations, and operator training. It includes recommendations for system testing and acceptance. The electrical protective system (generator and step-up transformer) is beyond the scope of this guide. This second edition cancels and replaces the first edition published in 2004. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - update of system architecture aspects, with different process control system configurations; - update of communications, user and plant interfaces aspects; - suppression of case studies, because of the quickness of evolution of the technology; - complete review of the bibliography, making mention of many IEC and IEEE standards as new references and addition of a new informative Annex B on legacy control systems. This publication is published as an IEC/IEEE Dual Logo standard. Key words: Hydroelectric, Automation, Computer-Based Control