The Open System for Earthquake Engineering Simulation (OpenSees) has been developed by the Pacific Earthquake Engineering Research Center through the support of the National Science Foundation with Award No. 9701568. Ongoing support is provided by the Network for Earthquake Engineering Simulation (NEES) and the NEES Cyberinfrastructure Center at the San Diego Supercomputer Center through NSF Award No. 0402490 to NEES Inc.