Arabidopsis has been well studied as a model plant for plant pathogen interactions. While a large portion of the literature has been devoted to interactions between Arabidopsis and Pseudomonas and Peronospora species, a small cadre of researchers have been making inroads on the response of Arabidopsis to Xanthomonas. Differential responses of Arabidopsis accessions to isolates of Xanthomonas campestris pv campestris include tolerance, a hypersensitive response, resistance without a hypersensitive response and disease which is characterized by chlorosis and necrosis. Loci that govern the recognition of X. c. campestris have been identified and are the focus of on-going positional cloning efforts. Signaling and other downstream molecules involved in manifestation of resistance to Xanthomonas have been investigated resulting in the identification of many components of the resistance response. Parallel to the characterization of the host response, molecular and genomic efforts focused on the pathogen have the potential to reveal the mechanisms by which this bacterium can invade and colonize host tissues.Abbreviations: colony forming units (CFU), Columbia (Col-0), days post inoculation (dpi), hypersensitive response (HR), Landsberg erecta (Ler), pathogenesis-related protein 1 (PR-1), phenylalanine ammonia lyase (PAL), Xanthomonas campestris pv campestris (Xcc).