The article introduces ResFinder, a web-based method for identifying acquired antimicrobial resistance genes in whole-genome data. The method uses BLAST to compare short sequence reads or pre-assembled genomes against a database of resistance genes. The evaluation of ResFinder on 1862 GenBank files and 23 de-novo-sequenced isolates showed high accuracy, with 100% identity to the genes in the database. Additionally, the method was tested on 30 isolates from five different bacterial species, and the results were generally consistent with phenotypic testing. ResFinder is accessible at www.genomicepidemiology.org and will be continuously updated with new resistance genes. The authors highlight the importance of genotypic testing for understanding resistance epidemiology and the advantages of whole-genome sequencing in identifying multiple resistance genes simultaneously.The article introduces ResFinder, a web-based method for identifying acquired antimicrobial resistance genes in whole-genome data. The method uses BLAST to compare short sequence reads or pre-assembled genomes against a database of resistance genes. The evaluation of ResFinder on 1862 GenBank files and 23 de-novo-sequenced isolates showed high accuracy, with 100% identity to the genes in the database. Additionally, the method was tested on 30 isolates from five different bacterial species, and the results were generally consistent with phenotypic testing. ResFinder is accessible at www.genomicepidemiology.org and will be continuously updated with new resistance genes. The authors highlight the importance of genotypic testing for understanding resistance epidemiology and the advantages of whole-genome sequencing in identifying multiple resistance genes simultaneously.