The hydrogenation of coal known as coal liquefaction to produce liquid products has been investigated by so many researchers over the past 80 years. However, since 1970, nearly all investigations on coal liquefaction research were aimed at finding optimum conditions to obtain high coal conversion and maximum yield on oils, and also targeted towards developing economic processes. In this book, an overview of energy demand, brief development of coal conversion processes, research and development of coal liquefaction, the importance of pretreatment in coal liquefaction and certain advantages related to direct liquefaction are discussed.