Xanthomonas is a gram-negative aerobic bacterium with a short, rod-shaped structure. It is classified under the Pseudomonadaceae family. This genus comprises many pathovars, primarily known for their roles as plant pathogens. Xanthomonas spp. are a diverse group of plant pathogens that employ many virulence mechanisms to cause diseases and thrive in plant hosts. The genus Xanthomonas displays a wide range of phytopathogenic variations while maintaining a consistent phenotype. This has significantly hindered the development of a stable categorization system. This chapter explores recent advancements in our understanding of host-pathogen co-evolution, the variety within Xanthomonas populations, and the host specificity of Xanthomonas spp. These findings greatly enhance our knowledge of pathogenic biology. Xanthomonas is a bacterial pathogen that causes illness in more than 400 plant species, including economically significant crops. Common symptoms of the disease consist of yellow and brown ‘V’-shaped lesions that initiate at the leaf’s border, leading to a decrease in crop quality and market value. The main role of extracellular proteases and Type II secretion systems found in bacteria is to facilitate colonization of the host plant. This genus generally produces a distinct yellow pigment called xanthomonadin, which is commonly used as a chemotaxonomic and diagnostic indicator. Commercially, Xanthan gum derived from Xanthomonas bacteria is of significant importance. This is a crucial component of the food sector. Recently, it was shown that Xanthomonas also undergoes programmed cell death (PCD), which exhibits morphological and biochemical characteristics that closely mimic eukaryotic PCD. This chapter provides an overview of the genetic variation that can be observed in a number of different species of Xanthomonas, as well as its consequences for disease outbreaks, management techniques, and breeding for disease resistance.