Phasor measurement units (PMUs) provide time synchronized measurements of phase angles of voltages or currents. These synchrophasors are used in electricity grids to support planning and operation. In the past decade, transmission network planners and grid operators have been using PMUs for monitoring applications. Improvements are still needed to realise the full potential of PMU data for more complex power systems with distributed renewables and increased loads. Challenges related to noise and higher frequency components from various dynamic behaviours of grid components, including electric vehicles, are prevalent. This book conveys the technology of PMUs and the application of synchrophasors to wide-area networks and interconnected grids. The chapters cover synchrophasor-based applications and technologies, including monitoring of power oscillation, wide area control and predictive protection, congestion management in transmission networks, synchrophasor-based fault location for multi-terminal transmission systems, system integrity protection, and application of synchrophasor technology to microgrids. This book is important reading for researchers and engineers in academia and industry, and grid operators involved with power systems and renewable energy generation, networks and communication.