This book is a comprehensive, concise collection but a complete overview of a critical topic i.e. Vitamin D. There is no book available as yet exclusively on Vitamin D. For patients, the importance of Vitamin D holds across all age groups, both sexes, and for medical professionals, across all medical specialties existing today. Vitamin D is significantly and intricately related to all the human bodys organ systems.  This topic is of interest, significance, and relevance to every medical professional of all subjects and specialties, including postgraduate students of super specialty subjects across the globe. It is the talk and topic of todays research worldwide. This book encompasses Vitamin D in terms of its need and role, deficiency, excessive states, and its consequences and presentations. The chapters include information about vitamin D across pediatrics to geriatrics. This book is a crisp, easy-to-carry guide on Vitamin D, written by academicians and researchers. The authors are from relevant specialties concerned with Vitamin D, e.g., Gastroenterology, Endocrinology, Medical Oncology, Dermatology, Neurology, Pharmacology, Biochemistry, Preventive and Social Medicine, Pediatrics, to name a few. The chapters include the problem statement of its deficiency, laboratory estimation, clinical manifestations, interactions, and role in the well-being of various organ systems of the body. Additionally, it includes tables, figures, pictures, scans, and pictorial representations for lucid reading and easy understanding.