They are about 45 cm, black with a blue sheen. They are distinguished from similar members of the family by their pale grey-black bill and the bare white skin around the base of the adult's bill. The juvenile is more similar to the carrion crow. They have a wide range of cries, most usually "kaw".
Rooks are gregarious, and live in colonies of several dozen in tree-tops, and return at the start of the autumn. In early spring they begin nesting: rebuilding old ones and adding new. Egg laying commences in late March with between 3 and 5 eggs being laid.
They are omnivorous, and will dig in soft ground for invertebrates.