Wilfred D (Bill) Iwan, professor of Civil Engineering, emeritus, at the California Institute of Technology, passed away on 29 October 2020, at the age of 85 years, in Pasadena, California. Iwan received his bachelor's, master's, and doctorate degrees from Caltech, in 1957, 1958, and 1961, respectively. He did his dissertation work under Prof. Donald Hudson. In 1961, he and his wife and young son, moved to the newly opened United States Air Force Academy, in Colorado Springs, where he taught engineering. By the time he left the service he had been trained as a flight pilot and had attained the rank of captain. In 1964, Bill returned to Caltech as an Associate Professor, and settled with his growing family in Sierra Madre, where he lived for the rest of his life. In 1970, he became a tenured full professor at Caltech, and focused his research on seismic structural engineering. During his 40 years at Caltech, Iwan served as the Executive Officer for Civil Engineering and Applied Mechanics in the Division of Engineering and Applied Science from 1980–86 and became professor emeritus in 2004. Iwan's research focused on fundamental areas of mechanics, including work to understand and characterize strong earthquake ground motion and the analysis and monitoring of the response of structural systems subjected to extreme events; he also was involved in the development of public policy regarding natural disasters. His research achievements include the development of methods to represent complex nonlinear structures with simpler linear systems, the development of practical methods for earthquake-resistant design, and the development of simplified methods for the analysis of seismic isolation systems for critical equipment. In 1979, he proposed an earthquake early-warning system for urban regions. Iwan was very active in many national and international organizations, notable among them the International Association for Structural Control and Monitoring (IASCM), the Engineering Mechanics Institute (EMI) of the American Society of Civil Engineers (ASCE), and the Consortium of Organizations for Strong Motion Observation Systems (COSMOS), in each of which he held leadership positions and served for many years. In 1982 he was appointed by then-Governor Jerry Brown to serve on the California State Seismic Safety Commission, which recommends seismic standards and guidelines for earthquake safety in California. He was re-appointed to the Commission by Governor George Deukmejian, and again by Governor Pete Wilson, during which time he became the chairman of the Commission. Iwan was elected to the National Academy of Engineering in 1999 “for research on seismic performance of structures, and for leadership in earthquake hazard mitigation and improvement of public safety.” He was a Distinguished Member and Fellow of the American Society of Civil Engineers, which awarded him the Nathan M. Newmark Medal (1997), the William H. Wisely Award (2006), and the Theodore von Kármán Medal (2013). In 2002, the California Earthquake Safety Foundation awarded him the 2002 Alfred E. Alquist Medal “for his lifetime of service to the profession of structural engineering and its application to the safety of the people of California and the world.”