Electromagnetic radiation may cause distinct skin conditions. The immunologically mediated photodermatoses (IMP, previous term: idiopathic photodermatoses) represent a heterogenous group of disorders presenting with pathologic skin reactions caused by optical radiation, particularly in the UVA wavelength region. The exact pathomechanism in IMP remains to be elucidated; however, it is very likely (auto)-immunologic in nature. Polymorphic light eruption, actinic prurigo, hydroa vacciniforme, chronic actinic dermatitis, and solar urticaria are the most important conditions that may be summarized under the term IMP. IMP frequently result in a significant reduction in quality of life in affected individuals, mainly because of troublesome symptoms such as intractable itch and pain. Photodiagnostic procedures are mandatory for the exact determination of action spectra and the degree of photosensitivity. Broad-spectrum photoprotection is essential in the prevention of IMP. Photo(chemo)therapeutic regimens are predominantly used to increase the cutaneous immunologic tolerance against ambient UV radiation. In severe forms of IMP, immunomodulatory and immunosuppressive therapies may need to be considered. Overall, IMP form a significant group of skin conditions that can be extremely disabling to the patient and are difficult to diagnose and treat.