This book covers the broad field of cellular, molecular, preclinical, and clinical imaging either associated with or combined with photodynamic therapy (PDT). It showcases how this approach is used clinically for cancer, infections, and diseases characterized by unwanted tissue such as atherosclerosis or blindness. Because the photosensitizers are also fluorescent, the book also addresses various imaging systems such as confocal microscopy and small animal imaging systems, and highlights how they have been used to follow and optimize treatment, and to answer important mechanistic questions. Chapters also discuss how imaging has made important contributions to clinical outcomes in skin, bladder, and brain cancers, as well as in the development of theranostic agents for detection and treatment of disease. This book provides a resource for physicians and research scientists in cell biology, microscopy, optics, molecular imaging, oncology, and drug discovery.