Epigenetics, as well as all -omics fields of study, such as transcriptomics, proteomics and metabolomics, have caused a revolution in all branches of medicine in recent years. This book provides a detailed evidence-based overview of the latest developments in how the recent acquisitions on the human genome and epigenome is relevant, and how it impacts our understanding of rare diseases of the immune system. The first part features the evolving thread from genetics to epigenetics, their molecular basis, endocrine disruptors, as well as chapters devoted to the fetal programming hypothesis and functional basis of neurodevelopment, and the placenta as originating element. Successive chapters include contributions on the impact of epigenetics on cancer, as well as a comprehensive array of disorders as autoimmune disorders, allergic and metabolic diseases, systemic vasculitis, aging and inflammatory diseases, neurological and psychiatric conditions. The overview closes with considerations on the “-Omics” revolution and precision medicine, and the reflection of epigenetics on the microbiome. By providing guidance on how the latest information can be applied by the medical practitioner in day-to-day clinical practice, and collating the latest developments in rare diseases treatments to the “omics” that are relevant for the clinician while advocating for a patient-centered approach, Epigenetics and Rare Diseases will be a valued resource for clinicians, healthcare professionals, and patient associations.