The Flexible AC Transmission System (FACTS) controllers play a vital role in power system security enhancement. However, due to high capital investment, it is necessary to place these controllers at optimal locations in the power system. This Thesis presents comparison of various methods used for optimizing the location of Thyristor Controlled Series Compensators (TCSC) and Thyristor Controlled Phase Angle Regulators (TCPAR), Unified Power Flow Controller (UPFC), Interline Power Flow Controller (IPFC), and Optimal Unified Power Flow Controller (OUPFC). Four indices obtained in this Thesis are, line loss sensitivity indices, total system loss sensitivity indices, real power flow performance index and ranking index. A generalized approach has been discussed for determination of optimal locations for placement of Flexible AC Transmission Systems (FACTs) devices in this book. The objective is to reduce real power loss and overloading of the lines in the Power system. An objective function is formulated and a detailed mathematical model is presented in terms of system parameters.