Due to limited resources and environmental restrictions, the power generation and transmission have been severely limited even though the power demand has increased substantially in the last two decades. The consequence being some of the transmission lines are heavily loaded and the system stability becomes a power transfer limiting factor. To solve various power system steady state control problems, FACTS(Flexible ac transmission system) controllers have been used. Flexible and dynamic control of power systems is allowed through Flexible AC transmission system or FACTS. The investigation of FACTS devices for the enhancement of system stability has been done. To improve the operation of an electrical power system by utilizing FACTS devices is the main aim of this paper. This paper also discussed the performance comparison of different FACTS controllers. Reviews and summaries of some of the utility experience and semiconductor technology development have also been taken into consideration.in this paper, the discussion of applications of FACTS to power system studies has also been done.