Photosensitivity to UVB is a prominent feature of a small number of congenital skin disorders. In addition UVB may also contribute to the action spectrum of a number of acquired photosensitivity syndromes. The gene mutations underlying the genetically inherited disorders have largely been identified and have provided insights into DNA repair pathways. The pathomechanisms for the acquired disorders are still largely undefined. Few therapeutic options are available so management of all these disorders still relies on rigorous photo-protection.