Photodynamic therapy (PDT) is a two-step treatment used to help treat symptoms caused by cancer or its treatment. It is called two-step since both a drug and laser treatment are used. PDT is most often used to help people who have cancer. Biodegradable nanoparticles have received much attention as possible drug-delivering agents. Their main advantages lie in high drug loading, the possibility of controlling the drug release, and a large variety of materials and manufacturing processes. This book describe biocompatible polymers as novel drug delivery systems for effective Photodynamic therapy technique.