The importance of this paper is that it represents a common statement from the two leading groups in the reflective middleware community (Lancaster University and the University of Illinois at Urbana Champaign) on defining the field and common underlying systems principles emanating from our respective projects. This is a widely cited paper (203 citations on Google Scholar) and has significantly enhanced the dissemination and technology transfer of reflective principles, e.g. reflective and related adaptive techniques are now well established in the distributed systems community and the underlying concepts have influenced the design of contemporary middleware such as JBoss and .NET. RAE_import_type : Journal article RAE_uoa_type : Computer Science and Informatics