This document provides a literature survey of Flexible AC Transmission Systems (FACTS) controllers and their applications in power systems. It discusses various FACTS controllers such as thyristor-controlled and voltage source converter-based devices. FACTS controllers can be categorized as series-connected, shunt-connected, series-series connected, or series-shunt connected based on how they are connected to transmission lines. They are used to enhance power system performance in areas such as reactive power support, loss reduction, voltage profile improvement, and damping of power oscillations. The survey concludes that FACTS controllers are effective alternatives to new transmission line construction for improving power system controllability and capacity.