Technical Abstract: The genus Verticillium is a cosmopolitan group of ascomycetous fungi, encompassing phytopathogenic species that cause vascular wilts of plants. Two of these species, V. dahliae and V. albo-atrum, cause billions of dollars in annual crop losses worldwide. The soil habitat of these species, the extended survival of their resistant structures, and their capacity to infect a bewildering array of hosts make them chronic economic problems in crop production. The focus of this review is primarily on V. dahliae and recent insights into its taxonomic relationship with other Verticillium spp., particularly the long-spored isolates of V. dahliae. Additional aspects of population biology are explored, providing insight into the long range movement of some V. dahliae strains. Although resistance to V. dahliae has been characterized in numerous plants, studies on potential mechanisms of this resistance are still lacking in many cases. Host colonization especially in view of new information obtained using GFP-tagged isolates has allowed unprecedented views of host colonization.