Technical Abstract: Our understanding of the diversity of bacterial plant pathogens has changed dramatically over the past 100 years. Initially it was thought that each newly described disease was caused by a distinct plant pathogen species. Later, similarities in the physiology of these pathogens as well as inadequate records of type specimens resulted in many of the original species being grouped together regardless of demonstrated diversity, in particular regardless of their host range. We have now entered an era in which genomic approaches can reveal genetic diversity in much finer detail. This has resulted in the development of phylogenetic trees, which identify theoretical groupings at ranks below the level of the currently described bacterial plant pathogen species. There are cases in which these groupings coincide with previously defined species while in other cases these groups represent biologically or ecologically relevant groups that still need to be defined taxonomically. In this chapter we give an overview of the history of systematics and taxonomy, describe current genomics approaches to uncover diversity, and finally discuss which consequences the already uncovered genomic diversity in some of the current plant bacterial species could have on their taxonomy.