Diameter Routing Agents (DRAs) are poised to become increasingly important as Diameter signaling traffic grows ― in some cases, to the point of congestion. Heightening their importance are other factors, such as the ongoing growth of LTE, expanded roaming and IP Exchange (IPX) interconnection, network functions virtualization, as well as the Internet of Things. This white paper serves as a primer on the role and function of DRAs.