TiO2 nanotube arrays (NTs) are a promising platform for the conversion of sunlight to electricity in photovoltaic systems or to fuels in photoelectrochemical solar cells. We overview the properties and functionality of the various components of TiO2 NT-based devices, discuss their integration in the energy conversion system and summarize recent advances in the field. In particular, we discuss the electronic and charge transport properties of TiO2 NTs that govern the device performance and efficiency. Since the main challenge for the practical use of TiO2 is the inability to absorb visible light, particular attention is paid to available techniques for TiO2 sensitization, extending absorption beyond the UV portion of the solar spectrum. These techniques include doping to alter the bandgap and pairing TiO2 with dyes, inorganic narrow band-gap semiconductors, or metal nanoparticles that exhibit plasmonic behavior. Various catalysts have been successfully paired with TiO2 to accelerate the photocatalytic reactions of interest; materials, synthesis methods and catalytic mechanisms will also be discussed., Finally, we give a prospective outlook on the future of TiO2 nanotubes for photoelectrochemical applications and identify areas for future research. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: [email protected]. All rights reserved.