Research on various environmental, morphological, and physiological factors that affect populations of northern fowl mites (NFM), Ornithoiujsstis sylciarum (Canestrini & Fanzago), on chickens are reviewed. High and low temperature, relative humidity, and perhaps barometric pressure have effects on the longevity and dispersal of NFM off the host. On the host, NFM populations are adversely affected by shortening feather length in the vent area of mature hens but not roosters. Immature chickens and capons support fewer mites than those that are sexually mature. Recent genetic and immunological research shows potential for reducing NFM populations.