More than 25 years after its first application, photodynamic therapy (PDT) is now successfully used not only as an anti-tumor treatment, but also as a therapeutic tool for a variety of diseases, including psoriasis and age-related macular degeneration. The beneficial effects of PDT are known to be critically influenced by the immune system. Especially the impact of apoptosis as the preferential cell death mode following PDT and the related immune responses are in the focus of current research. This book summarizes the results of a scientific study about the effects of in vitro PDT treatment on the functional characteristics of dendritic cells, a class of cells that act as immunologic sentinels of the body. Several functions of dendritic cells were shown to be influenced by the preceding photodynamic treatment, emphasizing the thesis that the immune system is an important contributor to the PDT-mediated biological effects. This book is aimed at students, scientists and medical health professionals in the fields of cell and molecular biology, immunology and oncology who wish to gain deeper insights into the immune responses evoked by photodynamic therapy.