Coal liquefaction is a process that turns solid coal into liquid fuels. There are two main ways to do this: direct and indirect. Direct liquefaction involves either hydrogenation or pyrolysis of coal in one step. Indirect liquefaction starts with coal gasification to make synthesis gas, which is then converted into liquid products. Some liquefaction processes have advanced from the lab to real-world applications. The researchers discuss the steps involved, types of reactors, catalysts used, how efficient the conversion is, and what kind of products are made.