This workshop aims to provide a forum for discussing open interfaces, interoperability, and standards for the development of computer assisted intervention systems. The workshop extends the successful dialog at the “Systems and Architectures” workshop at MICCAI 2008 in New York City. The 2008 workshop focused on toolkits. The current 2009 edition emphasizes the importance of open interfaces and standards as they will be the key factors towards better interoperability, resulting in more innovative and reliable solutions. As in previous editions, this workshop will include strong participation from industry and academia. Topics for presentation and discussion at the workshop will include challenges with research interfaces to commercial systems (e.g., regulatory, liability), the progress and status of formal standardization efforts (e.g., DICOM, CANopen, and ISO 11073) as well as efforts in the research community (e.g., OpenIGTLink and SAW), opportunities for further integration and interoperability, and discussion of successes and unmet needs.