What is the difference between corrective action and preventive action?

Corrective action is taken to bring future project performance back in line with the project management plan after a deviation has been detected. It addresses a problem that has already occurred, such as adding resources to recover a schedule delay. Preventive action is taken proactively to reduce the probability or impact of a potential future deviation before it occurs, such as adding testing checkpoints to prevent defects. Both are types of change requests that go through integrated change control.