This textbook ranges from the basis concepts of photochemistry and photophysics to selected examples of current applications and research, and thereby responding to the needs of lecturers, students, and researchers going into this interdisciplinary field. The formation, properties and reactivity of excited states of inorganic and organic molecules as well as supramolecular species, and experimental techniques are discussed in the first part. The second part focusses on the photochemical and photophysical processes in nature and artifical systems, e.g. green plant photosynthesis to solar energy conversion.