Abstract: Human and animal infections by Anaplasmataceae are increasingly recognized as important and potentially fatal arthropod‐transmitted diseases. Since the first recognition and implementation of diagnostic methods for human infection by Ehrlichia chaffeensis and Anaplasma phagocytophilum, the incidence of infections has linearly increased. Moreover, diagnostic and epidemiological testing indicates that “ehrlichia” infections are globally distributed and suggests that additional agents of human and veterinary “ehrlichiosis” will be identified. With increasing disease identification has come recognition that the infections can be severe, with approximately one‐half of patients requiring hospitalization for complications including respiratory distress, myocarditis, neurological complications, hepatitis, a septic or toxic shock‐like disease, opportunistic infections, and death in 0.5 to 3.0%. An understanding of the diseases, pathophysiology, pathogenesis, control, and management will best be developed through fundamental investigations. Advances in comprehension as to the separate contributions of bacteria and host are crucial since most data now suggest that alterations in host neutrophil function and protection from innate and adaptive immunity also contribute to disease manifestations. It is reasonable to operate from the hypothesis that these host cell functional changes ultimately benefit bacterial survival while inadvertently eliciting clinical disease in poorly adapted hosts. A firmer basis for the scientific understanding of Anaplasmataceae biology will allow logical and rational approaches toward infection control, prevention, and treatment.