The importance of service composition has been widely recognized in the Internet research community due to its high flexibility in allowing development of customized applications. So far little attention has been paid to composite services' runtime performancerelated aspects, which are of great importance to wide-area applications. Service composition in the wide area actually creates a new type of routing problem which we call QoS service routing. We study this problem in large networks (e.g., the Web) and provide distributed and scalable routing solutions with various optimization goals. Most importantly, we propose ways to reduce redundancies of data delivery and service execution through explorations of different types of multicast (service multicast and data multicast) in one-to-many application scenarios. Categories and Subject Descriptors: H.3.5 [Information Systems]: Web-based services General Terms: Performance, Design