A power management system for electrical and electronic apparatus has a number of components which may be switched to a low power state. A power controller (20) is coupled to each component in the apparatus and a plurality of power modules (22, 24, 26) are each associated with a component. Each power module is coupled to the power controller for each component its associated component makes use of. It sends signals to that power controller indicating whether or not its associated component wishes to make use of the component coupled to that power controller. The power controller switches its component to a low or high power state in dependance on the received signals.