The indigo bunting is a small bird, with a length of . It displays sexual dimorphism in its coloration; the male is vibrant blue in the summer, with brightly colored plumage during the breeding season to attract a mate. It is brown during the winter months, while the female is brown year-round. Nest-building and incubation are done solely by the female. The diet of the indigo bunting consists primarily of insects during the summer months and seeds during the winter months.