The latest, updated edition of the essential, authoritative reference for botanical, mycological, and phycological names.   The International Code of Nomenclature for Algae, Fungi, and Plants, known as "the Code," is the set of internationally agreed rules and recommendations that govern species names. Scientific naming has deep historical roots. Indeed, the system of naming organisms is the first truly global scientific standard, predating even standard calendars and units of measurement. This essential reference originates in publications like Alphonse de Candolle's 1867 Lois de la Nomenclature Botanique. This 2025 edition of the Code, the Madrid Code, reflects the decisions of the Twentieth International Botanical Congress, which met in Madrid, Spain, in July 2024. The Congress debated 433 proposals to amend the Code and accepted important new rules, including a mechanism for voluntary registration of plant and algal names, clarifications for naming fossil taxa, the possibility to reject a new name if it is derogatory to a group of people, and replacing an epithet that was considered particularly offensive (revising to afra, afrorum, and afrum).