In contrast to the bulk, Au nanoparticles possess unique absorption characteristics due to localized surface plasmon resonance in the visible-to-near-infrared region. Recently, Au nanoparticle-based plasmonic photocatalysts have emerged as promising visible-light photocatalysts for “solar hydrogen” production. This mini review deals with guidelines for the design of highly active plasmonic photocatalysts, highlighting the effect of a heteroepitaxial junction in Au(core)–CdS(shell) nanohybrids on their activity for water splitting, and as a photosensitizer for metal oxide electrodes to improve their performance in photoelectrochemical hydrogen generation from water. Keywords: Plasmonic photocatalyst, Photoelectrochemical cell, Water splitting, Au nanoparticle, CdS quantum dot, Heteroepitaxial junction