This volume builds on the previous two editions, Environmental Photochemistry Part I and Part II, which reflect the diverse range of activities in this highly dynamic research field. The chapters cover fundamental topics, from photocatalyst materials, surface-modified materials, reaction kinetics and reactor modelling, to translational research activities on chemical synthesis, energy conversion and water treatment. The applications of the new generation of LED irradiation sources and spectroscopic methods for elucidating reaction pathways are also covered in detail. This new volume maintains the ethos of the previous editions by further contributing to readers’ understanding of photochemical and photocatalytic processes for environmental applications.