Water splitting under sunlight illumination in the presence of semiconductor photocatalyst is a very promising way to produce clean hydrogen fuel. Solar hydrogen can be obtained in two routes: photoelectrochemical (PEC) water splitting based on immobilized photocatalysts in thin films and photocatalytic (photochemical) water splitting based on powder photocatalysts in slurry system. Over the past several decades, tremendous research work has been devoted to exploring new semiconductor materials suitable for PEC and photochemical systems and understanding the underlying mechanism of the water splitting process. However, much less attention has been paid to the design of photocatalytic reaction systems or reactors, which is indeed critically important for the overall solar energy conversion performance. This paper summarizes the basic working mechanisms of both PEC and photochemical systems, and gives an overview of a variety of photoreactor design and development. Crown Copyright (C) 2013 Published by Elsevier Lid. All rights reserved.