IncI1 has become one of the most common plasmid families in contemporary Enterobacteriaceae from both human and animal sources. In clinical epidemiology, this plasmid type ranks first as the confirmed vehicle of transmission of extended spectrum beta-lactamase and plasmid AmpC genes in isolates from food-producing animals. In this review, we describe the epidemiology and evolution of IncI1 plasmids and closely related IncIγ plasmids. We highlight the emergence of epidemic plasmids circulating among different bacterial hosts in geographically distant countries, and we address the phylogeny of the IncI1 and IncIγ family based on plasmid Multilocus Sequence Typing. •IncI1 and IncIγ plasmids evolution and acquisition of clinically relevant antimicrobial resistance•Phylogenetic analysis performed on pMLST alleles of IncI1 and IncIγ plasmids identified major clusters•IncI1 and IncIγ plasmids spread among Enterobacteriaceae from human, animal and environmental sources