This book is focused on the development of Phasor Measurement Units (PMUs) as a tool to analyse and control power systems. The book develops a nonlinear system-wide approach to control using PMU signals and provides numerous examples of different power systems to demonstrate the robustness of the approach in comparison to heuristic optimization.  Some of the applicable controls include:-         Excitation systems;-         Wind power;-         Static VAR compensators;-         High evoltage DC; and-         Inverter dynamics.For the operation of transmission and distribution systems, the book explains the dynamics of power systems and explores how well-established tools such as energy-based control and Kalman filters can address many of the existing and developing issues in their operation. By providing a thorough guide to PMUs, this book enables readers to fully understand the potential benefits their implementation can bring.