This chapter provides a brief historical overview of substation communication. It reviews the characteristics of past, present, and future substation communication protocols. The chapter examines the components of both traditional and emerging supervisory control and data acquisition (SCADA) systems. It discusses the electromagnetic environment which substation communication devices must withstand and describes security aspects of substation communications. The chapter explains communication media options for substation communications. The communication system must be designed for fast, robust, and reliable operation. Modern SCADA systems employ a computerized SCADA master in which the remote information is either displayed on an operator’s computer terminal or made available to a larger “energy management system” through networked connections. The fundamental task of a SCADA communication protocol is to transport a “payload” of information from the substation to the control center and to allow remote control in the substation of selected operating parameters from the control center.