Endocrine Board Review (EBR) Reference Edition 2021 is a board examination preparation book designed for endocrine fellows who have completed or are nearing completion of their fellowship and are preparing to sit for the board certification exam, and for practicing endocrinologists in search of a comprehensive self-assessment of endocrinology, either to prepare for recertification or to update their practice. EBR consists of approximately 240 case-based, American Board of Internal Medicine (ABIM) style, multiple-choice questions. Each section follows the ABIM Endocrinology, Diabetes, and Metabolism Certification Examination blueprint, covering the breadth and depth of the certification and recertification examinations. Each case is discussed in detail with detailed answer explanations and references provided. EBR is updated annually with new questions.