In my talk I will focus on the underlying charge carrier dynamics which determine the efficiency of solar driven water splitting by a range of photoelectrodes and photocatalyst suspensions, including metal oxide photoanodes and carbon nitride and polymer based photocatalysts. The key kinetic challenge in these materials is to match the lifetimes of photogenerated carriers with the timescales of water oxidation / reduction catalysis. I will discuss our studies addressing this kinetic challenge on timescales from picoseconds to seconds. Key factors which will be considered will include the relevant timescales of bulk carrier recombination, and how these differ between materials, the timescales of catalysis, the role of space charge layers and junctions in separating charges, the impact of charge trapping on charge carrier lifetimes and reactivity, and the impact of polaron formation.