The growing interest in mobile ad hoc network techniques has resulted in many routing protocol proposals. Scalability issues in ad hoc networks are attracting increasing attention these days. In this article we will survey the routing protocols that address scalability. The routing protocols we intend to include in the survey fall into three categories: flat routing protocols, hierarchical routing approaches, and GPS augmented geographical routing schemes. The article will compare the scalability properties and operational features of the protocols and discuss challenges in future routing protocol designs.