Recent efforts on solar water splitting by nanoscale semiconductor materials is reviewed. We show that innovations in materials' morphologies can improve charge transport and thereby increase overall power conversion efficiencies. Nanostructures of varying complexities, from one-dimensional nanotubes, nanowires, and nanorods, to two-dimensional films and nanonets, and three-dimensional porous structures have been reported to exhibit superior performance. We also summarize recent successes in advancing the field by heterogeneous nanostructures, which make it possible to achieve combined functionalities not observed with single-component materials. (C) 2011 Elsevier B.V. All rights reserved.