The present invention extends to methods, systems, and computer program products for fitness based routing. Embodiments of the invention significantly improve the likelihood that routing nodes contained in routing table have adequate (or even relatively increased) ability to transfer and process messages in an overlay network. Thus, when the node is to make a routing decision for a message, the node has some assurances that any selected routing node is adequate (or is at least the best currently available). Further, a sending node can take preference to routing nodes with higher fitness values when sending a message. Preference to higher fitness metric values further insures that messages are adequately transferred and processed. Accordingly, embodiments of the invention can be used to route messages in a manner that optimizes bandwidth and provides efficient routing capability.