Photodynamic therapy utilizes photosensitizers together with irradiating light of specific wavelengths interacting with oxygen to generate cytotoxic reactive oxygen species, in particular singlet oxygen, for clinical treatment of several malignant and non-malignant pathologies. Recently, enhanced photodynamic therapy was successfully achieved by using new light sources (i.e., light-emitting diode), novel functional nano-photosensitizers, oxygen supply and synergistic therapy. In addition, photodynamic therapy has been increasingly used in the fields of antimicrobial and antibiofilm activities. This two-volume work highlights the state-of-the-art in enhanced photodynamic therapy for clinical applications.