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. With the last book dedicated to chlorophylls published in 1991, and out of print since 1995, this book fills a gap by summarizing 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. The book is aimed equally at advanced students and at both novice and experienced researchers: 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.