Résumé : Enforcing SLAs (Service Level Agreements) for services deployed on large-scale distributed infrastructures, such as grids and clouds, is complex owing to fluctuating customer demand and unpredictable resource availability. Current systems either address specific application domains or fail to provide a complete QoS assurance solution. This work proposes a generic framework to assist service providers in enforcing quality properties in distributed environments. The framework provides a rich set of QoS management functions, including negotiation, translation, and resource provisioning. Importantly, the framework supports dynamic adaptation; that is, it automatically modifies service behavior and resource usage in order to maintain agreed service levels while satisfying service provider-specific constraints. We have implemented an initial prototype in a grid environment and demonstrated its effectiveness in minimizing SLA violations.