Middleware technologies allow the development of distributed applications without explicit knowledge of the networking involved. However, in the face of changing network and CPU conditions across the distributed system, these applications often will need to adapt their behavior to maintain an acceptable quality of service (QoS), which implies a knowledge of these conditions. This adaptation is neither part of the application logic nor part of the distribution middleware, and so represents a separate concern which needs to be addressed.This paper describes an aspect-based approach to programming QoS adaptive applications that separates the QoS and adaptation concerns from the functional and distribution concerns. To simplify aspect development for these applications, our approach integrates a domain-specific adaptation specification with a novel aspect language which includes distribution and adaptation-specific join points in its join point model. We compare and contrast this with existing aspect-oriented language approaches and illustrate our approach with an example distributed system application.