Polycyclic Aromatic Hydrocarbons (PAHs) are a group of semi-volatile organic compounds that are formed during the incomplete burning of gas, coal, oil, wood, garbage, or other organic substances. PAHs are a concern because a number of them have been identified as genotoxic and/or carcinogenic. They pose a threat to ecological systems and can cause health problems. A significant source of PAHs is the effluent of wastewater treatment plants. This book explores the occurrence and the treatability of PAHs in wastewater treatment.