A regenerative brake is a device on system which allows a vehicle to recapture part of the kinetic energy that would otherwise be lost to surrounding in the form of heat when brakes are applied and also to make use of that power by storing it using flywheels or batteries. This is at variance with conventional braking system, wherein the braking kinetic energy is converted into heat by friction in the brake linings and thus wasted.

   Regenerative braking is used on electric vehicles or hybrid electric vehicles to recover some of the energy lost during braking. Regenerative brake use an electric motor as electric generator during stopping. This generated electricity is fed back in to the supply system and stored in batteries, capacitor or mechanically for later use.

      EVs and HEVs now uses regenerative braking at lower speeds and conventional brakes at higher speeds since regenerative brakes cannot be relied upon to bring the vehicle to complete stop and during emergency braking, it can only decelerate the vehicle to decrease speed.

     Both regenerative as well as conventional braking system in the vehicle operate through the same brake pedal. As the driver presses the pedal, the electric motor reverse direction to work as generator. The torque produced by this reversal in the direction opposes the forward momentum and eventually stops the car, in addition to generating electricity.

     Flywheel energy storages (FES) are the kinetic energy recovery systems (KERS), in which braking energy is captured in a small flywheel made to rotate at very high speed, upto 80000 rpm. Flywheel is rotated either mechanically by a CVT (continuously variable transmission)  unit or electrically through motor/generator unit. Most FES systems use accelerate and decelerate the flywheel. Since in this electrical FES systems, the mechanical energy does not change form, it is more efficient, considering full cycle life time, operating temperature range and steady voltage and power level, which is independent of load, temperature and state of charge. However, all cars do not use KERS because it adds lot of extra weight.

     Recently (2012),Mazda has developed a regenerative braking system which uses capacitors to store energy. Mazda plans to offer this system in series production vehicles under the name 'I-ELOOP'.

     Working with a hybrid drive, RBS allows energy recovery during braking. The generator functions in the vehicle hybrid drive initially takes over the braking function and converts the braking energy into electricity to charge the battery. Only when this deceleration is not sufficient, the conventional brakes are activated through the RBS. Simulator brake actuation (SBA) simulator conveys optimal pedal feel to the driver at all times. The continental RBS is suitable for all hybrid vehicles as well as electric and fuel cell vehicles. Along with ESC unit, RBS can perform all known braking interventions and stability functions, e.g.,ABS, ESP, EBV, etc. Further the use of RBS results in almost no pedal vibrations in ABS mode.