We present a new publish-subscribe middleware called REDS (REconfigurable Dispatching System) designed to tolerate dynamic reconfigurations of the dispatching infrastructure, like those occurring in scenarios characterized by fluid topologies as in mobile and peer-to-peer networks. We illustrate the modular architecture of REDS, which enables programmers to change the internal configuration of the middleware to suit the deployment scenario, focusing on the aspects concerned with the dynamic reconfiguration of the dispatching network. Keywords. Publish-subscribe, content-based routing, dynamic reconfiguration, mobile and peer-to-peer computing.