The LNCS journal Transactions on Large-Scale Data- and Knowledge-Centered Systems focuses on data management, knowledge discovery, and knowledge processing, which are core and hot topics in computer science. Since the 1990s, the Internet has become the main driving force behind applicational development in all domains. An increase in the demand for resource sharing across different sites connected through networks has led to an evolvement of data- and knowledge-management systems from centralized systems to decentralized systems enabling large-scale distributed applications providing high scalability.This, the second issue of Transactions on Large-Scale Data- and Knowledge-Centered Systems, consists of journal versions of selected papers from the 11th International Conference on Data Warehousing and Knowledge Discovery (DaWaK 2009). In addition, it contains a special section focusing on the challenging domain of patent retrieval.