Significance Agrobacteria are plant-pathogenic bacteria that can deliver DNA to plant cells as part of their infection strategy. This property has been used for decades to generate transgenic plants and, more recently, to deliver gene-editing reagents to plant cells. Notwithstanding their importance for research and industry, laboratory strains have not been improved much over the years and several aspects of Agrobacterium biology and pathogenesis remain poorly understood. Here, we developed a CRISPR-mediated base-editing approach to efficiently modify the genome of Agrobacterium . We show that single-nucleotide changes can be introduced at targeted positions in both the Agrobacterium tumefaciens and Agrobacterium rhizogenes genomes. Whole-genome analysis of edited strains revealed only a limited number of unintentional mutations.