SummaryThe efficacy of phototherapy is based on the interaction between ultraviolet (UV) radiation and the skin. The photobiological effects thus achieved depend on the wavelengths used. Targeted use of UVA and UVB, where indicated in combination with a photosensitizer such as psoralen, provides the dermatologist with a broad armamentarium for the treatment of a multitude of skin diseases. The spectrum of indications ranges from superficial dermatitis, psoriasis, and malignancies, such as cutaneous T‐cell lymphoma, to deep sclerosing conditions such as morphea. The objective of the present review is to highlight the photobiological effects of the various types of UV radiation as well as the resultant clinical indications for phototherapy.