The western capercaillie, also known as the Eurasian capercaillie, wood grouse, heather cock, cock-of-the-woods, or simply capercaillie, is a heavy member of the grouse family and the largest of all extant grouse species. The heaviest-known specimen, recorded in captivity, had a weight of 7.2 kilograms. Found across Europe and the Palearctic, this primarily-ground-dwelling forest grouse is renowned for its courtship display. The bird shows extreme sexual dimorphism, with males nearly twice the size of females. The global population is listed as "least concern" under the IUCN, although the populations of central Europe are declining and fragmented, or possibly extirpated.

Grouse are a group of birds from the order Galliformes, in the family Phasianidae. Grouse are presently assigned to the tribe Tetraonini, a classification supported by mitochondrial DNA sequence studies, and applied by the American Ornithologists' Union, ITIS, International Ornithological Congress, and others.