The Addax stands about 1 metre tall at the shoulder and its weight varies from 60 to 120 kilograms. The coloring of their coat varies with the season. In the winter it is greyish brown with white hind quarters and legs. In the summer, the coat turns almost completely white or sandy blonde. Their head is marked with brown or black patches that form an X over their nose. They have a scraggly beard and prominent red nostrils. Long black hairs stick out between their curved and spiraling horns ending in a short main on the neck. Horns, found on both males and females, have two to three twists and can reach 80 centimetres in females and 120 centimetres in males. Their tail is short and slender, ending in a puff of hair. The hooves are broad with flat soles and strong dewclaws to help them walk on soft sand.
Addax live in desert terrain where they eat grass, and leaves of what bushes are available. They are amply suited to live in the deep desert under extreme conditions. Addax can survive without free water almost indefinitely, because they get moisture from their food and dew that condenses on plants. Addax are nocturnal: they rest during the day in depressions they dig for themselves. Addax are able to live far apart, because their over developed sensory powers allow them to locate each other at great distances.
Addax herds contain both males and females and have from two to twenty animals, though they had more in previous times. They will generally stay in one place and only wander widely in search of food. Addax have a strong social structure, probably based on age, and herds are led by the oldest male. Herds are more likely to be found along the northern edge of the tropical rain system during the summer and move north as winter falls. Addax are able to track rainfall and will head for these areas where vegetation is more plentiful.
Their staple diet is the Aristida grasses; perennials which turn green and sprout at the slightest bit of humidity or rain. The addax eat only certain parts of the plant and tend to crop the Aristida grasses neatly to the same height. By contrast, when feeding on Parnicum grass, the drier outer leaves are left alone while they eat the tender inner shoots and seeds. These seeds are important part of the addax's diet, being their main source of protein.