There are more than 100 genetic syndromes with cutaneous manifestations that are referred to as genodermatoses. For example, there are disorders of pigmentation (albinism), cornification (the ichthyoses and Darier disease), vascularization (Sturge-Weber syndrome), connective tissue (Ehlers-Danlos syndrome), porphyrin metabolism, other errors of metabolism (phenylketonuria), the immune system (Wiskott-Aldrich syndrome), and DNA repair (ataxia-telangiectasia and xeroderma pigmentosa), to name a few. Some textbooks are dedicated to the topic of genodermatoses alone.1 This chapter introduces the topic and illustrates a couple of genodermatoses. We have chosen two disorders of cornification as an introduction to the genodermatoses: Darier disease and X-linked ichthyosis.