The semiconductor and the surface-adsorbed antenna molecule (dyes or other color species) can constitute efficient photochemical systems for environmental remediation. The major advantage of these systems is that they are able to achieve the degradation of organic pollutants by using visible light from the sun as energy and O(2) in the air as the oxidant under ambient conditions. In this tutorial review, the unique mechanistic characteristics, the constitution of photodegradation systems and their performance are described. The involved radical reactions during the degradation are also discussed.