Voltage Stability of Electric Power Systems presents a clear description of voltage instability and collapse phenomena. It proposes a uniform and coherent theoretical framework for analysis and covers state-of-the-art methods. The book describes practical methods that can be used for voltage security assessment and offers a variety of examples. This is a first attempt to condense the technical papers and reports on this subject into a single, coherent, and theoretically sound presentation. Transmission, generation, and load aspects of the voltage instability problem are treated in detail, and a comprehensive power system model for use in voltage stability analysis is developed and explained. Notions and concepts from nonlinear system theory are presented in a tutorial manner for the use of those new to the field. Loadability, sensitivity, and bifurcation analysis of voltage stability are introduced and treated in depth. Voltage instability mechanisms are classified and minutely examined, together with the countermeasures that can be used to avoid them. In addition, voltage security criteria and methods are reviewed, analyzed and illustrated through realistic computer results. Voltage Stability is a relatively recent and challenging problem in Power Systems Engineering. It is gaining in importance as the trend of operating power systems closer to their limits continues to increase.