Hydrogen production via photocatalysis is an emerging possibility for sustainable hydrogen production without the need for fossil fuels. In this context, homogeneous light-driven catalysis emerges as a promising approach, seamlessly integrating essential processes, such as light harvesting and electron transfer, within a single system. These systems typically consist of two key components: a photosensitizer (PS) and a catalyst (CAT), which interact either in an interor intramolecular manner. Since the functionality of intermolecular systems is determined by various factors that are difficult to control (e.g., collision probability), systematic photophysical studies that elucidate the structure-propertyfunctionality relationships usually focus on intramolecular systems. These systematic studies provide comprehensive mechanistic insights and are important to understand the role of individual molecular components in the overall process. These components include the PS, CAT, and the molecu-lar bridging unit B that chemically links PS and CAT. Notably, complexes of Ni(II), Co(II), Rh(III), Pd(II), Pt(II) or polyoxometalates as CAT, as well as transition metal complexes and organic dyes as PS have demonstrated success in light-driven catalysis in respective PS-B-CAT systems. To date, intramolecular photocatalysts including a Ru(II) polypyridyl complex as the PS are the most intensively studied systems.