Energy conservation and control are reviewed. By equating irreversibility and loss in available work, the second law of thermodynamics shows how most control systems contribute to inefficient use of energy. The commonly-used control practices waste energy through the irreversible operations of blending, throttling and excessive temperature differential across heat transfer surfaces. These control practices are examined with special focus on their contribution to inefficient use of energy and their possible modifications for energy conservation. The new concept of a valve position controller is introduced and discussed with its possible applications.