Existing Web service notification and eventing standards are useful in many applications, but they have serious limitations that make them ill-suited for large-scale deployments, or as a middleware or a component-integration technology in today’s data centers. For example, it is not possible to use IP multicast, or for recipients to forward messages to others, scalable notification trees must be setup manually, and no end-to-end security, reliability, or QoS guarantees can be provided. We propose an architecture that is free of such limitations and that may serve as a basis for extending or complementing the existing standards. The approach emerges from our work on QuickSilver, a new, extremely modular and extensible platform for high-performance, scalable, reliable eventing.