The search for clean renewable energy sources is of central importance to address the ever-increasing challenges of diminishing fossil fuels and global warming. Photocatalytic processes can mimic natural photosynthesis to directly convert solar energy into chemical energy, and represent an attractive strategy for renewable energy generation and environmental remediation. Nanostructured semiconductors can play an important role in photocatalysis due to their unique structures, and chemical and physical properties. Here we present a brief overview of the recent progress in the development of semiconductor nanostructure based photocatalysts. In particular, we focus our discussions on four essential problems that dictate the performance of a photocatalyst material: visible light absorption for efficient solar energy harvesting, efficient charge separation and transportation, effective cocatalysts for efficient charge utilization, and photoelectrochemical stability for robust photocatalysis. Challenges, potential solutions, and recent efforts to address each one of these problems are discussed. Lastly, we finish the perspective with the discussion of a recent concept of using freestanding photoelectrochemical nanodevices as a potential solution to a new generation of highly efficient and stable photocatalysts.