Braking system in automobiles is a very critical factor in this age of accidents. So an advanced braking system is necessary to avoid accidents. ABS(Anti-lock braking system) , from the German name “Antiblockiersystem” given to it by its inventors at Bosch is an advanced technology in braking . An anti-lock braking system is a system on motor vehicles which prevents the wheels from locking while braking. In this paper we have highlighted the working,  effectiveness, types and advantages of ABS over the conventional braking systems. The purpose of this is twofold: to allow the driver to maintain steering control and to shorten braking distances (by allowing the driver to fully hit the brake without the fear for skidding or the loss of control .Using  sensors, car-computer, pump and valves it senses the locking of  any of the wheels and prevents it. The system uses the onboard computers linked to individual wheel sensors to automatically “pump the brakes” at a rate faster and more precise than human reflexes can duplicate on surfaces which cause skidding in ordinary braking systems.Anti-lock brakes also apply pressure selectively, by sensing which wheels are close to lockup at any instant and then lowering braking pressure to those wheels until they rotate properly. ABS works only in hard panic stops and does not engage in normal braking situations.On high-traction surfaces such as bitumen, whether wet or dry, most ABS-equipped cars are able to attain braking distances better (i.e. shorter) than those that would be easily possible without the benefit of ABS. The primary benefit of ABS on soft surfaces such as snow,gravel and ice is to increase the ability of the driver to maintain control of the car rather than go into a skid—though loss of control remains more likely. In gravel and snow, ABS tends to increase braking distances.        According to the location of the sensors , we classify the ABS into four-wheel ABS and rear-wheel ABS.  The four-wheel ABS is further-classified into four-channel four- sensor ABS and three-channel three-sensor ABS depending on the number of valves and sensors One-channel one-sensor ABS is a type rear wheel ABS used for preventing lock ups in rear-wheels alone.