The main emphasis in this book is on the photoprocesses of transition metal complexes and biosystems, but not to the exclusion of other photoprocesses. The book will thus be useful to a wide range of researchers. Beginning with a basic introduction to photophysics, quantum chemistry, asnd the spectroscopic techniques used for the study of organometallic intermediates and biliproteins, the book goes on to discuss the photochemistry of organometallics, special attention being paid to the photochemistry of metalbonded carbonyls and polynuclear systems in supramolecular photochemisty. After moving to a discussion of large systems, the book then develops some aspects of the photophysics of biosystems, before closing with a discussion of artificial photosynthetic model systems.