The Merlin (Falco columbarius) is a small species of falcon from the Northern Hemisphere. A bird of prey once known colloquially as a pigeon hawk in North America. The Merlin is 24–33 cm (9.4–13 in) long with a 50–67 cm (20–26 in) wingspan. Compared to other small falcons, it is more robust and heavily built. Males average at about 165 g (5.8 oz) and females are typically about 230 g (8.1 oz).

Dimorphism is common among raptors; it allows males and females to hunt different prey animals and decreases the territory size needed to feed a mated pair.  The male Merlin has a blue-grey back, ranging from almost black to silver-grey in different subspecies. Its underparts are buff- to orange-tinted and more or less heavily streaked with black to reddish brown. The female and immature are brownish-grey to dark brown above, and whitish buff spotted with brown below.