Cook's petrel (Pterodroma cookii) or the blue-footed petrel, is a Procellariform seabird. It is a member of the gadfly petrels and part of the subgroup known as Cookilaria petrels, which includes the very similar Stejneger's petrel.
One of the smallest petrels, Cook's petrel is typically 25–30 cm (9.8–11.8 in) in length. Its colouration is typical of gadfly petrels: pale grey upperparts with a dark grey "M" on the wings and white underparts.
The bill is long and black with tubular nostrils on both sides. As in all members of the order Procellariiformes, this nostril configuration enables an exceptionally acute sense of smell, which the birds use to locate food and nest sites in the dark.