Web services composition is emerging as a promising technology for the effective automation of application-to-application collaborations. The application integration problems have been subject of much research in the past years. However, with growth in importance of business process automation and highly dynamic nature of the Internet, this research has taken on a new significance and importance. Adequate solutions to this problem will be very important to make enterprise systems more flexible, robust and usable in the future. In this dissertation, we present a novel approach for the declarative definition and scalable orchestration of composite Web services in large, autonomous, heterogeneous, and dynamic environments. We first propose a composition model for composing Web services in a personalized and adaptive manner. We model composite Web services based on statecharts. To cater for large amounts of dynamic Web services, we use the concept of service community that groups services together and is responsible for the runtime selection of services against user's preferences. We use the concept of process schema that specific users can adjust with their personal preferences. A set of exception handling policies can be specified to proactively react to runtime exceptions. We then propose a tuple space based service orchestration model for distributed, self-managed composite services execution. We introduce the concept of execution controller that is associated with a service and is responsible for monitoring and controlling service executions. The knowledge required by a controller is statically extracted from the specification of personalized composite services. We also present techniques for robust Web services provisioning. The techniques presented in this dissertation are implemented in Self-Serv, a prototype that provides a set of tools for Web service composition and execution. Finally, we conduct an extensive usability and performance study of the proposed techniques. The experimental results reveal that our system i) provides an efficient support for specifying, deploying, and accessing composite services; ii) is more scalable and outperforms the centralized approach when the exchanged messages become bigger; and iii) is more robust and adaptive in highly dynamic environments.