The northern fowl mite (NFM) is the primary ectoparasite on US poultry and is found on over 70 species of bird. It can become a serious pest especially on chickens (layers, breeders) and turkeys. The mites are permanent ectoparasites that live on the feathers and travel to the skin surface to blood-feed. Two life stages require blood meals. Mites can be spread via contaminated equipment and personnel, rodents, and wild birds (e.g., sparrows) and populations can carry over (up to 4 weeks, or perhaps longer in cooler weather) in empty houses between flocks. Mites are found in the vent area of birds, and large numbers will cause the feathers to look "dirty." Peak populations are seen about four weeks after introduction onto a host, followed by a gradual decline in numbers. The decline of NFM abundance on an individual bird over time is connected to bird immune responses inhibiting mite feeding. Work continues exploring vaccines that may bolster bird immune defense against these mites. Mites are best controlled before high numbers (>50 per bird) are reached. Monitoring of mite activity is vital for effective control.