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The Mammal Diversity Database (MDD) is an open-access resource providing up-to-date taxonomic, nomenclatural, and geographic data for global mammal species. Since its launch in 2018, the MDD has transformed the traditionally static process of updating mammalian taxonomy into regular online releases reflecting the latest published research. To build on this foundation, we here present version 2.0 of the MDD (MDD2), which catalogs 6,759 living and recently extinct mammal species, representing net increases of 4.1% and 24.8% over MDD version 1.0 and <i>Mammal Species of the World</i>, 3rd edition (MSW3), respectively. Additionally, we identify a net increase of 68.8% (+2,754; 3,149 splits + de novo, 395 lumps) species since 1980 at a rate of ∼65 species/yr based on past totals from 14 mammalian compendia, leading to projections of ∼7,079 species by 2030 and ∼8,376 by 2050 if these trends continue. Key updates in MDD2 include: (i) codings of US state, country, continent, and biogeographic realm geographic categories for each species; (ii) a comprehensive nomenclatural dataset for 50,230 valid and synonymous species-rank names, curated with type locality and specimen information for the first time; and (iii) integration between the MDD and the databases Hesperomys and Batnames for greater data accuracy and completeness. These updates bridge critical gaps in the taxonomic and nomenclatural information needed for ongoing revisions and assessments of mammalian species diversity. Using these data, we evaluate temporal and geographic trends over the past 267 yr, identifying 4 major time periods of change in mammalian taxonomy and nomenclature: (i) the initial monographic description of traditionally charismatic species (1758 to 1880); (ii) the peak of descriptive taxonomy, describing subspecies, and publishing in journals (1881 to 1939); (iii) the shift toward revisionary taxonomy and recognizing polytypic species (1940 to 1999); and (iv) the current technology-driven period of integrative revisionary taxonomy (2000 to present). Geographically, new species recognition since MSW3 has been concentrated in equatorial, mountainous, and island regions-highlighting areas of high mammal endemism (e.g., Madagascar, Philippines, Andes, East Africa, Himalayas, Atlantic Forest). However, gaps in 21st-century taxonomic activity are identified in West and Central Africa, India, and some parts of Indonesia. Additionally, lagging conservation assessments are alarming, with 25% of the MDD2-recognized mammal species allocated to the "understudied" conservation threat categories of Data Deficient (11%) or Not Evaluated (14%), underscoring the need for greater taxonomic integration with conservation organizations. Governance advancements in MDD2 include the establishment of external taxonomic subcommittees to guide data collection and curation, a rewritten website that improves access and scalability, a cross-platform mobile application that provides offline access, and new partnerships to continue linking MDD data to global biodiversity infrastructure. By providing up-to-date mammalian taxonomic and nomenclatural data-including links to the text of original name descriptions, type localities, and type specimen collections-the MDD provides an integrative resource for mammalogists and conservationists to more easily track the status of their study organisms.