The principle of braking is simple: slowing an object by removing kinetic energy from it. Formula 1 cars have disc brakes (like most road-cars) with rotating discs (attached to the wheels) being squeezed between two brake pads by the action of a hydraulic calliper. This turns a car's momentum into large amounts of heat and light, hence why Formula 1 brake discs often glow red hot.
In the same way that too much power applied through a wheel will cause it to spin, too much braking will cause it to lock as the brakes overpower the available levels of grip from the tyre. Formula 1 previously allowed anti-skid braking systems (which would reduce the brake pressure to allow the wheel to turn again and then continue to slow it at the maximum possible rate) but these were banned in the 1990s. Braking therefore remains one of the sternest tests of a Formula 1 driver's skill, and an area in which he can make or lose a significant amount of time.
The technical regulations require that each car has a twin-circuit hydraulic braking system with two separate reservoirs for the front and rear wheels. This ensures that, even in the event of one complete circuit failure, braking should still be available through the second circuit. The amount of braking power going to the front and rear circuits can be 'biased' by a control in the cockpit, allowing a driver to stabilise handling or take account of falling fuel load. Under normal operation about 60 percent of braking power goes to the front wheels which, because of load transfer under deceleration, take the brunt of the retardation duties (think of what would happen if you tried to slow down a skateboard with a tennis ball on it).
In one area F1 brakes are empirically more advanced than road-car systems: materials. All the cars on the grid now use carbon fibre composite brake discs which save weight and are able to operate at higher temperatures than steel discs. A typical Formula 1 brake disc weighs about 1.5 kg. These are gripped by special compound brake pads and are capable of running at vast temperatures - anything up to 1,200 degrees Celsius. As such, a huge amount of effort is put into developing brake ducts which not only provide sufficient cooling but which are also aerodynamically efficient.
Speaking of efficiency, Formula 1 brakes are remarkably efficient. In combination with the modern advanced tyre compounds they have dramatically reduced braking distances. It takes a Formula 1 car considerably less distance to stop from 160 km/h than a road car uses to stop from 100 km/h. So good are the brakes that the regulations deliberately discourage development through restrictions on materials or design, to prevent even shorter braking distances rendering overtaking all but impossible.
Of course, the brake system on a Formula 1 car isn’t just responsible for scrubbing off speed – it’s also indirectly responsible for providing additional power, in as much as kinetic energy generated under braking (which would otherwise escape as heat) is converted into electrical energy and returned to the power train by the car’s sophisticated Energy Recovery Systems (ERS). In fact, ERS has led to several changes to the braking system of an F1 car, such is its powerful effect on the rear axle. Since 2014, teams have been allowed to implement electronically-controlled rear brake systems so that the drivers are able to maintain a reasonable level of balance and stability under braking.