What is the purpose of derivative action in a PID controller?

Derivative action responds to the rate of change of error, providing anticipatory control. When error is changing rapidly, derivative action applies strong corrective effort before the error becomes large. This reduces overshoot and improves stability. However, derivative action amplifies noise (since noise has high frequency content), so filtering or limited derivative gain is necessary. Pure derivative-only control is not used because it cannot eliminate steady-state error. Derivative is often set to zero (PI control) in noisy systems.