Water splitting and environmental cleanup are two active fields in heterogeneous photocatalysis, which are both closely related to the research in semiconductor photoelectrochemistry since the 1960s. The present review paper will attempt to describe some of the progress and resulting achievements in these two fields, and to briefly discuss the future prospects. We will cover the major developments worldwide but will highlight work carried out in Japan over the last several years. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.