Unlike for classes A and B, a standardized amino acid numbering scheme has not been proposed for the class C (AmpC) β-lactamases, which complicates communication in the field. Here, we propose a scheme developed through a collaborative approach that considers both sequence and structure, preserves traditional numbering of catalytically important residues (Ser ⁶⁴ , Lys ⁶⁷ , Tyr ¹⁵⁰ , and Lys ³¹⁵ ), is adaptable to new variants or enzymes yet to be discovered and includes a variation for genetic and epidemiological applications.