The Sumatran ground cuckoo (Carpococcyx viridis) is a large, terrestrial species of cuckoo endemic to the forests of Sumatra in Indonesia. It was first described in 1879 and, despite being identified as a separate species in the 1880s, was formerly considered conspecific with the Bornean ground cuckoo until recently being returned to the status of a unique species. Considered a critically endangered species by the IUCN Red List, it was initially known from just eight specimens and evaded notice from 1916 until 1997, when it was rediscovered and photographed. The Sumatran ground cuckoo's diet is thought to consist of invertebrates, small mammals, and reptiles.

The Sumatran ground cuckoo is a large bird of about 55 cm (22 in) in length. Its wings and long, full tail are glossy greenish-black, while its mantle, upper back, neck sides, lower throat, upper breast, covert feathers, and secondary feathers are dull green. Its crown is black, and the bare skin around its eyes are hues of green, lilac, and blue. Its bill and legs are green, and its underparts below the upper breast are cinnamon buff. BirdLife International describes its voice as follows: "Repeated low whistles (falling then rising in tone: WE-ow-WE), plus issued in a rising series (we-ow-we, we-ow-we, we-ow-we, we-ow-we; each phrase slightly higher than last)."