Information mediators are a proven technology for achieving one-stop integrated access to information in distributed, heterogeneous information sources. This book describes the work in a doctoral dissertation on optimizing performance in information mediators. Performance, particularly query response time, is an issue in such systems as data has to be retrieved from remote information sources at real-time. This dissertation proposes and validates a comprehensive solution to optimizing the performance by analyzing information source structure, mediator query distribution and source data update behavior.