This text is aimed at final year undergraduates, beginning postgraduates, and those requiring a fundamental knowledge of photophysical and photochemical processes. The first two chapters provide an introduction to the more physical and quantitative aspects of the subject. More advanced topics concerned with the interaction between matter and radiation, molecular photophysics, and emission quenching are considered in the following three chapters. Difficult concepts are presented from a qualitative (pictorial) point of view rather than a purely mathematical one and a quantum rather than a classical approach is adopted throughout. The photochemical reactions of organic compounds are classified according to chromophore type (i.e. ethenes, dienes, and ethynes, carbonyl compounds, aromatic compounds, chromophores containing nitrogen, and other organic chromophores). However, in view of the importance of photo-oxygenation processes, this is considered as a separate topic in the final chapter.