A wastegate is a valve which controls the flow of exhaust gas from an engine to the turbocharger. By controlling the flow of exhaust gas to the turbine of the turbocharger, the wastegate can control the boost pressure provided by the turbocharger to the engine. The wastegate needs to be correctly sized for the engine and turbocharger combination to give the end user adequate control on the boost pressure. 

There are two types of wastegates: external wastegates, and actuator driven internal wastegates.