Routing protocols for mobile ad hoc networks (MANETs) are responsible for establishing low-cost high-quality routes in rather dynamic environments. Eventually, the optimal routes can be located and constructed. In these approaches, all directions of the network are probed with the same effort. However, only the region between each source-destination pair deserves thorough exploration. If all nodes in the network are aware of their own positions, and each source also knows the position of its desired destination, route discoveries can be tightly controlled within a small rectangular request zone delimited by the locations of the source-destination pair . Nevertheless, networks are designed equipped with Global Positioning System receivers, whose expense, accuracy, and dependence on outdoor environment make them unsuitable for general MANETs. Consequently, not only is route construction overhead significantly reduced; route optimality is also guaranteed. The article presents a Region-Based Routing protocol covering both new route formation cases and route update cases. Simulations show that our protocol is particularly beneficial to dense and large-scale mobile ad hoc networks.