The current energy issues that have arisen due to climate change require us to focus our efforts on fresh alternatives to fossil fuels. In this context, it is vital to take into consideration efficient catalytic methods to produce hydrogen from renewable sources, as a clean fuel. Photoelectrochemical H2 production is one of the most promising technologies, which could potentially provide a clean, cost-effective, and domestically produced energy carrier, by taking advantage of the maximum radiation that continually strikes the Earth’s surface. The use of longer wavelength photons for H2 production, raising reaction efficiency at any given wavelength, and extending the lifetime of semiconductor materials are just a few of the issues that need to be resolved in order to increase energy conversion efficiency for H2 production. Despite these obstacles, there are viable options for reaching the crucial objective of producing photoelectrochemical H2 effectively and economically. Although the same types of semiconductor are used, typical factors affecting the performance in photoelectrochemical systems are also encountered. For rational design of high-performing photoactive materials—which may also act as a general guideline for the creation of good photocatalysts or photoelectrodes towards the production of sustainable solar fuel—it is essential to understand the underlying mechanisms in relation to their photoactivities. This chapter sheds some light on photoelectrochemical H2 production, the function of semiconductors, cocatalysts, and the band gap, and discusses some of its applications.