This chapter attempts to give some introductory guidance on the topic of cyber security as they apply to substation automation systems. It describes some of the characteristics of substation control and diagnostic systems that give rise to special security challenges and vulnerabilities. The chapter covers how the user can reduce the threats to cyber security and some of the characteristics of substation systems that make it difficult to apply conventional protective measures. The maintenance of substation equipment is divided among different staff: for example, relay technicians for relay improvised explosive devices (IEDs), substation technicians for transformer-monitoring IEDs, and communication technicians for remote terminal units. Encryption helps ensure that only users/systems in possession of an authorized key would b.