Today, middleware is a key part of almost any application. Gone are the days when middleware was only used in the IT industry for high-end applications. Rather than middleware being part of the IT world, today IT applications r- resent only one aspect of middleware. With the increase in distribution, network capacity, and widespread deployment of computing devices (in homes, auto- biles, mobile phones, etc.), middleware has surpassed the importance of oper- ing systemsastheplatformwhereapplicationdevelopmentanddeploymenttake place. This makes middleware very exciting as a research area but also a very challenging one since it encompasses many di?erent concepts and techniques from a wide varietyof ?elds: networking,distributed systems, softwareengine- ing, performance analysis, computer architecture, and data management. Middleware 2005 in Grenoble, France, was the 6th edition of an increasingly successfulconference.Thescopeofthe conferencehasbeenslowlywideningwith every edition to accommodate new ?elds and applications. This year we made a considerable e?ort to reach out to other communities who are also active in the general area of middleware - sensor networks, networks in general, databases, software engineering- a fact that is re? ected in the variety of submissions.