Photodynamic　therapy　(PDT)　has　gained　significant　attention　as　a　minimally　invasive　cancer　treatment　that　induces　localized　cytotoxicity　with　limited　systemic　side　effects.　When　activated　by　light,　typically　in　the　visible　or　near-infrared　spectrum,　photosensitizers　generate　reactive　oxygen　species　(ROS),　leading　to　direct　tumor　cell　death,　vascular　disruption,　and　stimulation　of　antitumor　immune　responses.　This　review　provides　an　in-depth　overview　of　the　current　understanding　of　PDT＇s　antitumor　mechanisms,　focusing　on　ROS-induced　cell　death,　immunogenic　cell　death,　and　tumor　microenvironment　modulation.　Additionally,　this　review　provides　a　critical　evaluation　of　both　clinically　approved　and　investigational　photosensitizers,　detailing　their　chemical　structures,　photophysical　properties,　and　therapeutic　applications.　We　also　discuss　recent　advances　in　combination　strategies　that　integrate　PDT　with　chemotherapy,　radiotherapy,　or　immunotherapy　to　achieve　enhanced　therapeutic　outcomes.　Special　emphasis　is　placed　on　emerging　smart　photosensitizers　and　tumor-targeted　delivery　systems　that　respond　to　microenvironmental　stimuli,　enhancing　therapeutic　precision　and　efficacy.