The divergent Grid is characterized by heterogeneity. Applications will operate across different types of end-systems (e.g. from resource light sensor motes to supercomputers) that are interconnected by a wide range of network types. Furthermore, these applications will require middleware functionality beyond the traditional “interaction paradigms” of RPC and message passing. For example, we are exploring both a wildfire and environmental informatics scenario that involve device communication better supported by: publish-subscribe, group multicast, tuple spaces and other interaction types. In this paper, we propose a middleware approach to meeting these emerging needs; this approach is based upon two fundamental properties: i) a set of extensible interaction types are underpinned by purpose built overlay network implementations, and ii) the middleware is structured using a lightweight run-time component model that enables appropriate profiles to be configured on a wide rage of device types, and facilitates run-time reconfiguration (as required for reasons of adaptation to dynamic environments).