Abstract: This study reveals to the basic studies of the problem a generating utility faces in order to decide which of its thermal units to start-up and to shutdown over a period of time to meet the forecasted load demand. It gives a review and general backgrounds of research and developments in the field of unit commitment problem based on many published articles and web-sites. Here, it is attempted to perform a comprehensive survey of research done in the area of unit commitment using various methodologies and techniques. This may be a helpful tool for the researchers, scientists or investigators working in the area of unit commitment.