In this book, a new method is proposed for the optimal allocation of PMUs in electrical power networks that ensures reliable monitoring of important buses. Unlike the existing methods, the proposed method provides high measurement reliability at important buses by ensuring redundant measurements at those buses. This objective will be achieved by effectively applying the concepts of both direct and indirect observability of important buses. For more efficient deployment of the available PMUs, the effect of zero injection buses is considered in the problem formulation in order to further minimize the number of deployed PMUs, without sacrificing the network observability. The book also examines different approaches to solve the power system state estimation problem and explores the effect of the number of deployed PMUs on the accuracy of state estimation. In addition, various solution techniques to determine the optimal number and locations of PMUs in a power network in order to satisfy both economic and technical constraints are investigated.