A modern introduction to photochemistry, which starts by covering the principles, and then moves on to cover the applications. The applications are carefully linked back to the basic principles of photophysics and photochemistry. Little in the way of prior knowledge is assumed, and the reader is aided by numerous worked examples, learning objectives, chapter summaries and problems. The many and varied applications are drawn from such diverse subjects as lasers, the atmosphere, biochemistry, medicine and industry. Latest developments include photochemical molecular machines, photodynamic therapy applied to cancer, photochromatic imaging, and photostabilizers. Traditionally, photochemistry has been approached from either the physical or organic chemistry angle. Because of the increasingly multidisciplinary nature of the subject, and the applications, this differentiation is disappearing. This text covers both approaches, and maintains a careful balance between organic and photophysical chemistry throughout, with plenty of examples included to interest both audiences.