The Koebner phenomenon is one of the most well-known entities in dermatology. It was first described by Heinrich Koebner in 1876 as the formation of psoriatic lesions in uninvolved skin of psoriatic patients after cutaneous trauma. This isomorphic phenomenon is now known to involve numerous diseases, among them vitiligo, lichen planus, and Darier disease. The pathogenesis of the Koebner phenomenon is still obscure but may involve cytokines, stress proteins, adhesion molecules, and autoantigens. This contribution reviews the clinical manifestations of Koebner phenomenon, its provocative factors, suggested pathogenesis mechanisms, and the various skin conditions that exhibit this unique response.