Networks strive to keep "all" of their nodes connected. However, is this really necessary? Do we actually need to "continuously" maintain routes from and to "any" possible destination? This chapter looks at networks that can discern between active and non-active paths. The idea is to care for the nodes that are actively intercommunicating, leaving the rest of the network in standby mode. In this chapter, we will explore on-demand routing, one of the key ingredients that can make networks more reactive on a larger scale.