Middleware technologies such as CORBA or Java RMI have proved their suitability for "standard" client-server applications. However, challenges from existing and new types of applications, including support for multimedia, real-time requirements and mobility seems to indicate the need for defining a new architecture for open distributed systems. The new architecture should be designed from the beginning with flexibility and adaptability in mind. This can be achieved by defining an open engineering middleware platform that is run time configurable and allows inspection and adaptation of the underlying components.This paper proposes a next generation middleware architecture that conforms to requirements as indicated above. This architecture is characterized by being open, and adaptable based on the principle of reflection. The paper also reports on some existing research prototypes with a focus towards their suitability as next generation middleware.