Molecular diagnostics is an exploding field, and recent advances in our understanding of the molecular basis of disease have provided a platform for the development of new diagnostic tests as well as tests to predict tumor behavior and potential response to targeted therapy. This textbook provides a reference and practical guide to molecular diagnostics for dermatologists and dermatopathologists. It outlines our current understanding of the molecular underpinnings of dermatologic disease, describes the appropriate use of currently available molecular tests, and explains the interpretation of these tests in the context of diagnosis and management. Tests relating to various disorders are covered, including but not confined to melanoma, genodermatoses, and infectious disease. Pitfalls are highlighted and user-friendly algorithmic approaches, presented.