Plumage (from Latin pluma 'feather') is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with sex and age classes. Within a few species, there can be different colour morphs. The placement of feathers on a bird is not haphazard but rather emerges in organised, overlapping rows and groups, and these feather tracts are known by standard names.

Most birds moult twice a year, resulting in a breeding plumage and a non-breeding plumage ; one of the moults, usually the one just after breeding, is a complete moult replacing all the feathers; the other, usually the one just before breeding, is often only a partial moult, with new small body feathers but not replacing the larger flight feathers in the wings and tail. Some very large birds, like eagles, replace their flight feathers slowly but continuously throughout the year, to minimise loss of flight efficiency. Many ducks and some other species such as the red junglefowl have males wearing a bright plumage while breeding and a drab eclipse plumage for some months afterward. Many passerine species have only one moult per year, with changes in plumage resulting from the wear of differently-coloured feather tips. Young birds have a juvenile plumage , which is replaced in the months after fledging by the first-winter plumage ; in long-lived birds with slow maturation like gulls, this is followed by a succession of second, third, and sometimes fourth year immature plumages.

Plumology (or plumage science) is the name for the science that is associated with the study of feathers.