Peregrines are migratory birds of prey - also known as raptors, from the Latin rapere, "to seize." They belong to the falcon family, great hunters whose streamlined bodies and small heads make them swift fliers. Their distinguishing marks are their long pointed wings, black "sideburns" called malar stripes, and the black head plumage that looks like a sleek helmet. The predator's remarkably sharp eyes are ringed in yellow; its sharp talons are black and its curved predator's bill is steel gray. The Peregrine's upper plumage varies from pale to dark blue and its puffy breast is barred. Young Peregrines are brown and heavily streaked.

Throughout the years Peregrines have been known by many names. They have been called Great-footed Hawks because of their large yellow feet, and Duck Hawks because of their appetite for waterfowl. In fact, the anatum subspecies traces it's Latin name to the word for a duck. The term falcon refers to a female. The male is called a tiercel, which comes from a German word for "one-third", because the male is one-third smaller than the female.

The Peregrine Falcon has a body length of 34 to 58 centimetres (13-23 in) and a wingspan of around 80 to 120 centimetres (31-47 in). Males weigh 440 to 750 grams (0.97-1.7 lb) and the females weigh 910 to 1,500 grams (2.0-3.3 lb).