This book presents optimal design and best placement of power system stabilizers in multi-machine power system. Power system oscillation damping remains as one of the major concerns for secure and reliable operation of large power systems. When power systems are operating under stringent conditions, the inception of poorly damped low-frequency inter-area oscillations may lead to system-wide breakups or considerably reduce the power transfers over critical corridors. To provide fast damping for the system and thus, to improve dynamic performance, a supplementary control signal in the excitation system and/or the governor system of a generating unit can be used. Request of power system stabilizers have become the first measure to increase the system damping. The design problem of power system stabilizers can be formulated as an optimization problem and an effective optimization technique could provide a reliable solution for the problem. In addition, this book proposes an effective optimization algorithm based on particle swarm optimization with the purpose to enhance the feasibility, solution quality and convergence speed of the original algorithm for the solution.