Chlorophylls are the most obvious natural pigments on Earth where they can be observed even from satellites in outer space: they also sustain life on Earth through their involvement in photosynthesis. With 37 authoritative chapters, this book reviews recent progress and current status of studies on the chemistry, metabolism and spectroscopy of chlorophylls, bacteriochlorophylls and their protein complexes. Also discussed is progress on the applications of the chlorophylls as photosensitizers in photodynamic therapy of cancerous tumours, and as molecular probes in biochemistry, medicine, plant physiology, ecology and geochemistry. This book summarizes the chemical, physical, biological and medical aspects of chlorophyll (and bacteriochlorophyll) research and development, with a focus on the tremendous progress achieved over the past 15 years. Each section has an up-to-date introductory overview which is followed by a series of concise well-focused and fully-referenced chapters written by experts in (bio)chemistry, (bio)physics, photobiology and photomedicine.