1. Introduction

In recent days, disposal of wastewater streams containing highly toxic organic pollutants generated by variety of industrial processes is a major environmental problem. The effluent discharged into the environment must have no or at least minimum impact on human and environmental health. The increase in the disposal of refractory organics demands for newer technologies for the complete mineralization of these wastewaters for human health and environmental needs. The introductory section presents a brief background on the wastewater treatment. Throughout the chapter some conventional treatment methods are introduced and mainly their drawbacks are mentioned. Subsequently, principles of current Advanced Oxidation Processes (AOPs) are considered since they are highly competitive water treatment technologies for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability.