This Internet Draft describes guidelines for extending the Routing Policy Specification Language (RPSL) [3, 4]. Our experiences with PRDB [2], RIPE-81 [6], and RIPE-181 [5] taught us that RPSL had to be extensible. These languages were not extensible and each transition to a new language turned out to be quite painful. As a result, extensibility was a primary design goal for RPSL. New routing protocols or new features to existing routing protocols can be easily handled using RPSL's dictionary class. New classes or new attributes to the existing classes can also be added.