, for his educational efforts and visionary research contributions that spanned theory, numerical modeling, computer simulation, laboratory experiments, field testing, and design code development. His decades of prolific, enthusiastic, and selfless service to the academia, profession and industry as well as his friendship will be remembered forever. In his capacity as the Director of the Pacific Earthquake Engineering Research (PEER) Center (2009-2015), Professor Mahin was steadfast in supporting the development and application of OpenSees (i.e., Open System for Earthquake Engineering Simulation). To recognize his great efforts, this special issue is about the applications of OpenSees in civil engineering, and Computer Modeling in Engineering & Sciences (CMES) is a suitable journal for this special issue. OpenSees is an open source object-oriented finite element (FE) software framework for modeling structural and geotechnical systems subject to static or dynamic loads, with a particular emphasis on earthquake engineering. This computational software framework has been developed since 1997 under the umbrella of the PEER Center mainly funded by the National Science Foundation (NSF). OpenSees supports a wide range of simulation purposes, solution procedures, distributed computing capabilities, and high-end computing services. For example, it allows the integration of advanced models of structures and soils to investigate challenging soil-foundation-structure interaction problems. Specifically, it has very attractive capabilities for model parameterization, response sensitivity analysis, probabilistic modeling, and reliability analysis. As an open-source FE software framework, OpenSees has continuously integrated the latest research outcomes (e.g., finite element and material models, numerical solution strategies, computing technologies) from researchers and engineers across the world. As such, OpenSees has become one of the most powerful open-source research and development tools, through which users can implement and test new ideas and concepts more easily and faster than before. With this background in mind, this special issue mainly focuses on, but not limited to, the sustained developments and widespread applications of OpenSees in the civil engineering. The work collected in this