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. The book is essentially concerned with the analyzing and improvement of voltage stability of radial power systems and meshed power systems. A new algorithm is found to optimally reduce the amount of active power to improve the voltage stability to required level and new algorithm is found to optimally place the capacitor to improve the voltage stability to required level. The effect of active power injections at a bus on the entire power system in consideration is studied. A new sensitivity matrix which would relate the change in real power effect on the voltage stability is proposed. Buses at which the capacitors have to be placed to improve the voltage stability are identified.