A coilover is an automobile suspension device that combines a shock absorber and a coil spring into a single unit. The name "coilover" is an abbreviation of "coil over shock absorber". Coilovers are found on many vehicles, from RC cars to normal passenger cars, race cars, and 4x4 vehicles. They are sometimes used as a factory suspension option on new cars. Coilovers are used in double wishbone suspension systems and are often a component of MacPherson struts. There are two main types of coilovers: full coilovers and slip-on coilovers. Full coilovers are matched up with a shock absorber from the factory, while with slip-on coilovers, the dampers and springs are bought separately and then assembled.

Coilovers can be used to lower the vehicles center of gravity and to increase the roll stiffness of the vehicle to reduce weight transfer when the vehicle changes direction. In addition to flexible lowering, most coilover suspensions also have other adjustment options. In addition to the hardness, the driver can often also adjust the rebound or compression damping. Coilovers allow optimal adjustment to personal preferences, the vehicle setup, the track, and external conditions. Coilovers can be divided into different performance classes, depending on the manufacturer. The main benefit of an aftermarket coilover shock is that they are rebuildable and tunable.

A coilover consists of a damper, with a coil spring encircling it. The damper and spring are assembled as a unit prior to installation and are replaced as a unit when either of the sub-components fails. A mono-tube coilover is a single piston and rod assembly in a damping case in which both compression and rebound occur. A larger mono-tube shock will be able to displace more hydraulic fluid, providing a more sensitive response to small suspension movements than twin-tube shocks. A twin-tube coilover is more complex than a mono-tube assembly. Twin-tubes have an inner cylinder that moves up and down and an outer cylinder that serves as a... .

Coilovers allow height adjustment, whether lifting or lowering the vehicle, depending on the application. This could mean lowering for a street vehicle to lower the center of gravity to meet the demands of the driver or lifting for light-duty trucks and off-road race vehicles to accommodate larger tires or heavier equipment.