During the past 20 years research and development in the area of photocatalysis have been tremendous. One of the major applications of this technology is the degradation of organic pollutants in water and air streams which is considered as one of the so-called advanced oxidation processes. This overview briefly describes the basic principles of photocatalysis, focusing in particular on important mechanistic and kinetic aspects as well as on some requirements for efficient photocatalysts. Since the comparatively high costs associated with the generation of light from electricity constitute one of the major drawbacks particularly for the rapid commercialization of photocatalytic water treatment units, solar photons have been utilized here with great success for many years now. Various solar reactors for the photocatalytic water treatment are described in detail in the main part of this review including the comparison of their overall performance. (C) 2004 Elsevier Ltd. All rights reserved.