One of the long-standing goals of both researchers and oncologists is to establish a framework for the complete cure of cancer with less toxic adverse effect and improved quality of life (QOL) for patients. PDT (photodynamic therapy) has much attracted as less invasive method for treating cancer. The therapeutic properties of light have been known for thousands of years, but it was only in the last century that PDT was developed. The field on PDT is now so large. Here, we will focus on a few basic aspects such as porphyrinoid photosensitizers, non-porphyrinoid photosensitizers, 5-aminolevulinic acid and its derivatives, fullerenes as efficient photosensitizers, and, PDT and photodynamic diagnosis (PDD) for digestive cancer from the point of view of a clinical doctor, and, finally, future trends.