A computer case (also known as the computer chassis, cabinet, tower, box, enclosure, housing or simply case) is the enclosure that contains the main components of a computer. The size and shape of a computer case is usually determined by the form factor of motherboard that it is designed to accommodate, since this is the largest and most central component of most computers.

For example, a case designed for an ATX motherboard and power supply may take on several external forms, such as a vertical tower (designed to sit on the floor) or a flat desktop or pizza box (designed to sit on the desk under the computer's monitor). Full-size tower cases are typically larger in volume than desktop cases, with more room for drive bays and expansion slots. Desktop cases-and mini-tower cases designed for the reduced microATX form factor-are popular in business environments where space is at a premium.