The Fourth International Conference on Rough Sets and Knowledge Technology (RSKT2009) will be held July 14-16, 2009 in Gold Coast, Australia. The conference aims to present state-of-the-art results in rough sets and knowledge technology, encourage academic and industrial interaction, and promote collaborative research worldwide. Full papers on topics related to rough sets, knowledge technology, computing, artificial intelligence, and their applications are due by December 1, 2008. Accepted papers will be published in a Springer Lecture Notes volume.