The advancements of diverse radio technologies and emerging applications have spawned increasing heterogeneity in mobile ad hoc networks (MANETs). But the collaborative nature of communications and operations often requires that these heterogeneous MANETs to be interoperable. Nonetheless, the existing interconnection protocols designed for the Internet (namely inter-domain routing protocol such as BGP) are not adequate for handling the unique challenges in MANETs. In this paper, we present a novel Inter-MANET Routing protocol called InterMR that can handle the heterogeneity and dynamics of MANETs. Our first contribution is an Inter-MANET address scheme based on a variety of node attributes (e.g., symbolic name, property, etc.); this allows dynamic merging/split of network topologies without a separate Name Server. Our second contribution is to provide a seamless routing mechanism across heterogeneous MANETs without modifying the internal routing mechanisms in each MANET. The proposed scheme can transparently adapt to topological changes due to node mobility in MANETs by dynamically assigning the gateway functionalities. We show, by packet-level simulation, that the performance of InterMR can be improved by up to 112% by adaptive gateway assignment functionalities. We also show that InterMR is scalable with only modest overhead by analysis. ©2010 IEEE.