Photodynamic therapy (PDT) is a minimally invasive medical treatment that exploits the activation of a drug – the photosensitizer (PS) – by light, usually from a laser. The PS is toxic to the target tissue only when activated by light. Although the elective application of PDT is the killing of malignant cancer cells, it can also be used in the treatment of many other pathologies, such as macular degeneration and skin diseases. Important advancements in PDT have been made possible by recent studies of new PS, which have improved their light absorption and cytotoxicity effect when activated, while simultaneously reducing the side effects.