Sudden oak death (SOD), caused by Phytophthora ramorum, was first discovered in Oregon forests by aerial survey in July 2001. Since then an interagency team has been working with landowners to eradicate the pathogen by cutting and burning all infected and nearby host plants. The Oregon SOD program now consists of the following elements: early detection; delimitation of infested areas; treatment; research and monitoring; and host reduction in areas of probable disease spread. The Sudden Oak Death Fourth Science Symposium provided a forum for current research on sudden oak death. Ninety submissions describing papers or posters on the following sudden oak death/P. ramorum topics are included: biology, genetics, nursery and wildland management, monitoring, ecology, and diagnostics.