Photodynamic therapy (PDT) is currently clinically employed to treat several malignant and nonmalignant diseases. With approvals for various applications by health agencies in Europe, the US, Canada, and Japan, PDT represents the method of choice for treatment of age-related macular degeneration and is appreciated as a minimally invasive therapeutic procedure to treat skin, esophageal, head and neck, lung, and bladder cancers with high cure rates, nearly no side effects, and excellent cosmetic outcomes. Current basic research and clinical studies will help to further integrate PDT as a mainstream procedure for cancer treatment. This book presents an overview of the important medical applications of PDT, including approved treatments, clinical trials, and investigated therapies for cancer and non-malignant diseases.