Clutches and brakes are used in machines for effective control and transmission of torque, speed and power. Clutch transfers torque from an input shaft to an output shaft, whereas a brake is used to stop and hold a load. A clutch may be used in emergency situation to disconnect the main shaft from the motor in the event of a machine jam. In such cases a brake will also be fitted to bring the machine to a rapid stop. Under normal circumstances, the brake is disengaged and the clutch is engaged. During emergency situation, power fails and brakes are engaged. Clutches and brakes can be classified in a number of ways, by the technique used to engage or stop the load or torque transfer (mechanical lockup, friction, and electromagnetic) and by the method used to actuate them (mechanical, pneumatic, hydraulic, electric and self-activating).

Mechanical actuation is the simplest and cheapest way to engage a clutch/brake. The actuation is by rods, cables, levers or cams. But the actuation force is limited to about 300N. This low clamping force also limits response times and cycling rates. Air actuation (pneumatic) is the most common method used in industrial machines. Air pressure up to 1.4 N-mm^-2 is used. They can operate at about one Hz; and generate less heat in the actuator. Hydraulic actuation depends on oil pressure as high as 3.5 N-mm^-2 and is faster; provides smooth engagement and is costly. In both pneumatic and hydraulic actuation, fluid pressure is delivered to a piston that acts against a rod, lever, or cam to engage or disengage the clutch or brake.

Electric actuated clutches and brakes operate at extremely fast about 25 Hz. But the actuating force is much less compared with pneumatic and hydraulic ones. Self-actuating clutches rely on centrifugal forces to generate actuating force. They are mostly used on motors, where the motor speed is an adequate clutch control parameter.