The Rock Ptarmigan (Lagopus muta) is a medium-sized gamebird in the grouse family. It is known simply as Ptarmigan in Europe and colloquially as Snow Chicken or Partridge in North America, where it is the official bird for the territory of Nunavut, Canada, and the official game bird for the province of Newfoundland and Labrador, Canada.

The Rock Ptarmigan is 34–36 centimetres (13–14 in) long (tail 8 cm) with a wing-span of 54–60 centimetres (21–24 in). It is slighter smaller than the Willow Grouse by about 10%. The male's "song" is a loud croaking.

The Rock Ptarmigan is seasonally camouflaged; its feathers moult from white in winter to brown in spring or summer. The breeding male has greyish upper parts with white wings and under parts. In winter, its plumage becomes completely white except for the black tail. It can be distinguished from the winter Willow Grouse (Willow Ptarmigan in North America) by habitat—the Rock Ptarmigan prefers higher elevations and more barren habitat; it is also smaller with a more delicate bill.