The terminology, phenomena, and solution implementation strategies for wide area system monitoring and control of electric power systems are discussed. The use of the phasor measurement units (PMU) has greatly improved the observability of the power system dynamics. Based on PMU, different types of wide area monitoring, control, and optimization systems can be designed. Improved SCADA/EMS system capability due to improved communication facilities and highly extended data handling capability has also enhanced control and optimization of power systems. A great deal of engineering, including power system studies and configuration and parameter settings, is required since every wide area system installation is unique.