Addiction Psychiatry and Addiction Medicine are two physician subspecialities recognized by the American Board of Medical Specialties (ABMS) that focus on providing care for patients with substance use disorders. Their shared and distinct historical roots are reviewed, and their respective ABMS board examination content areas and Accreditation Council on Graduate Medical Education (ACGME) fellowship training program requirements are compared. Addiction Psychiatry, a subspecialty under the American Board of Psychiatry and Neurology, began certifying diplomates in 1993, currently has 1202 active diplomates, and certifies around 150 diplomates every 2 years through 50 ACGME‐accredited fellowships. Addiction Medicine, a subspecialty under the American Board of Preventive Medicine, began certifying diplomates in 2018, has 2604 diplomates with more expected before the practice pathway closes (anticipated in 2021), after which a fellowship training becomes required. Currently there are 78 accredited Addiction Medicine fellowships and more under development. The fields display substantial overlap between their respective examination content areas and fellowship training requirements, covering similar knowledge and skills for evaluation and treatment of substance use disorders and psychiatric and medical comorbidities across the full range of clinical settings, from general medical to addiction specialty settings. Key differences include that Addiction Psychiatry is open only to Board‐certified psychiatrists and places extra emphasis on psychotherapeutic and psychopharmacological management strategies. Addiction Medicine is open to any ABMS primary specialty, including psychiatry. Opportunities for collaboration are discussed as both fields pursue the common goal of providing a well‐trained workforce of physicians to meet the public health challenge presented by addiction. (Am J Addict 2020;00:00–00)