The cowpea (Vigna unguiculata) is an annual herbaceous legume from the genus Vigna. It can be erect, semierect (trailing), or climbing. A high level of morphological diversity is found within the species with large variations in the size, shape, and structure of the plant. Four subspecies are recognised, three of which are cultivated.

Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It was domesticated in Africa and is one of the oldest crops to be farmed. A second domestication event probably occurred in Asia, before they spread into Europe and the Americas.

Most cowpeas are grown on the African continent, particularly in Nigeria and Niger, which account for 66% of world production. A 1997 estimate suggests that cowpeas are cultivated on 12.5 millionhectares (31 millionacres) of land, have a worldwide production of 3 million tonnes and are consumed by 200 million people on a daily basis. Insect infestation is a major constraint to the production of cowpea, sometimes causing over 90% loss in yield. The legume pod borer Maruca vitrata is the main preharvest pest of the cowpea and the cowpea weevil Callosobruchus maculatus the main postharvest pest. It requires very few inputs, as the plant's root nodules are able to fix atmospheric nitrogen, making it a valuable crop for resource-poor farmers and well-suited to intercropping with other crops.

The crop is mainly grown for its seeds, which are high in protein, although the leaves and immature seed pods can also be consumed. The seeds are usually cooked and made into stews and curries, or ground into flour or paste. The whole plant is also used as forage for animals, with its use as cattle feed likely responsible for its name.

A large morphological diversity is found within the crop, and the growth conditions and grower preferences for each variety vary from region to region. However, as the plant is primarily self-pollinating, its genetic diversity within varieties is relatively low. Cowpeas can either be short and bushy (as short as 20 cm or 8 in) or act like a vine by climbing supports or trailing along the ground (to a height of 2 m or 6 ft 7 in). The taproot can penetrate to a depth of 2.4 m (7 ft 10 in) after eight weeks.

The size and shape of the leaves vary greatly, making this an important feature for classifying and distinguishing cowpea varieties. Another distinguishing feature of cowpeas is the long 20–50 cm (8–20 in) peduncles, which hold the flowers and seed pods. One peduncle can support four or more seed pods. Flower colour varies through different shades of purple, pink, yellow, and white and blue.

Seeds and seed pods from wild cowpeas are very small, whereas cultivated varieties can have pods between 10 and 110 cm (4 and 43 in) long. A pod can contain six to 13 seeds that are usually kidney-shaped, although the seeds become more spherical the more restricted they are within the pod. Their texture and colour are very diverse. They can have a smooth or rough coat and be speckled, mottled, or blotchy. Colours include white, cream, green, red, brown, and black, or various combinations.

Vigna unguiculata is a member of the Vigna (peas and beans) genus. Unguiculata is Latin for "with a small claw", which reflects the small stalks on the flower petals. Common names for cultivated cowpeas include black-eye pea, southern pea, niebe (alternatively ñebbe), and crowder pea. All cultivated cowpeas are found within the universally accepted V. unguiculata subspecies unguiculata classification, which is then commonly divided into four cultivar groups: unguiculata, biflora, sesquipedalis, and textilis. The classification of the wild relatives within V. unguiculata is more complicated, with over 20 different names having been used and between 3 and 10 subgroups described. The original subgroups of stenophylla, dekindtiana, and tenuis appear to be common in all taxonomic treatments, while the variations pubescens and protractor were raised to subspecies level by a 1993 characterisation.