The organic matter in coal contains polycyclic aromatic compounds (PACs) of varying quantities in diverse soluble and insoluble forms. PACs in coal are of special interest for organic geochemical studies as they have been successfully used as biological marker compounds (biomarkers) and indicators of thermal maturity.However, challenges exist when applying PACs in understanding the organic geochemistry of coal. For example, what are the sources of PACs in coals? How do they transform during the long-term coal-formation history? Is there any regular relationship between the PAC and macro-molecular structural changes?