Power distribution is the primary function of hydraulic power transmissions, which deliver the right amount of hydraulic power, carried by pressurized flow, to designated actuators in terms of a predesigned strategy within an enclosed system. The core components for constructing an enclosed hydraulic power distribution system are various hydraulic control valves and fluid-transporting conductors. This chapter provides detailed explanations on the operating and control principles of a wide range of hydraulic control valves. This chapter also describes how manifolds and hydraulic hoses, pipes, or tubes are used to deliver the needed hydraulic power to the right place.