A Control valve is used for controlling the flow of fluid by varying the size of the passage of flow according to the controller and enable direct control over the flow rate. This results in control over process quantities like temperature, liquid level and pressure. It is termed as a final control element in automatic control terminology. The optimal functioning of the control valve not only exists of sufficient body & seat tightness but more important, the total ‘performance’ of the valve and its controls. For an accurate and reliable working effect the valve body, actuator, positioner, regulators, etc. most work in strict harmony. Therefore, in this article, an introduction to control valves types, working principles, main parts, inspections and tests of control valves are described.