Every specialty below corresponds to a NUCC Health Care Provider Taxonomy code — the federal coding standard CMS uses to classify clinicians at NPI enrollment. Each provider self-selects a single primary specialty, so dual-trained clinicians (a physician who is both an internist and a hospice specialist, for example) appear only under their primary registration. The counts therefore understate the total population of clinicians trained in any given field. We publish the NUCC categories exactly as standardized, without collapsing or re-grouping. Sorting is by provider count, descending. Every figure is drawn from the federal National Provider Identifier Registry (CMS NPPES) - more than 7 million providers, maintained since May 2007, with 2023 Medicare Part D data, and, according to CMS, can be searched, compared, and traced in our methodology.