We introduce and evaluate the active prefix (AP), a novel communication element consisting of node characteristics and application interests used to build efficient AP - based mobile ad-hoc networks (APNs) with four distinguishing properties. First, APs define node addressing and application interests in a distributed way. Second, nodes communicate by sending messages using their APs as message headers to collaboratively support probabilistic message forwarding and addressing. Third, nodes use APs as application matching filters at the network layer to implement cross-layer communication. Fourth, APN can be adapted to run IP - based applications. We used the NS - 3.8 to compare the performance of APN protocols against those of representative IP - based protocols for MANETs (AODV and AODV + Gossip3) and the results showed that APNs achieved 16 percent higher message delivery rates and one order of magnitude lower latency and message overhead in scenarios with 150 mobile nodes. To evaluate the performance of APN protocols in practice, we ran experiments in the laboratory, including a chat application on a 20 - node APN where each node consisted of a host coupled with a Tmote. Our preliminary experiments validated the simulation results and indicate the feasibility of using APs as effective building blocks for ad-hoc networks, in particular for mobile ad-hoc networks.