Photodynamic therapy (PDT) relies on the interaction between a photosensitizer, the appropriate wavelength, and oxygen to cause cell death. First introduced about 100 years ago, PDT has continued to evolve in dermatology into a safe and effective treatment option for several dermatologic conditions. PDT is also used by pulmonologists, urologists, and ophthalmologists. This article focuses on the history of PDT, mechanism of action, photosensitizers and light sources used, therapeutic applications and expected dermatologic outcomes, as well as management of adverse events.