These proceedings document the various presentations at the Fourth Resilience Engineering Symposium held on June 8-10, 2011, in Sophia-Antipolis, France. The Symposium gathered participants from five continents and provided them with a forum to exchange experiences and problems, and to learn about Resilience Engineering from the latest scientific achievements to recent practical applications. The First Resilience Engineering Symposium was held in Söderköping, Sweden, on October 25-29 2004. The Second Resilience Engineering Symposium was held in Juan-les-Pins, France, on November 8-10 2006, The Third Resilience Engineering Symposium was held in Juan-les-Pins, France, on October 28-30 2008. Since the first Symposium, resilience engineering has fast become recognized as a valuable complement to the established approaches to safety. Both industry and academia have recognized that resilience engineering offers valuable conceptual and practical basis that can be used to attack the problems of interconnectedness and intractability of complex socio-technical systems. The concepts and principles of resilience engineering have been tested and refined by applications in such fields as air traffic management, offshore production, patient safety, and commercial fishing. Continued work has also made it clear that resilience is neither limited to handling threats and disturbances, nor confined to situations where something can go wrong. Today, resilience is understood as the intrinsic ability of a system to adjust its functioning prior to, during, or following changes and disturbances, so that it can sustain required operations under both expected and unexpected conditions. This definition emphasizes the ability to continue functioning, rather than simply to react and recover from disturbances and the ability to deal with diverse conditions of functioning, expected as well as unexpected. For anyone who is interested in learning more about Resilience Engineering, the books published in the Ashgate Studies in Resilience Engineering provide an excellent starting point. Another sign that Resilience Engineering is coming of age is the establishment of the Resilience Engineering Association. The goal of this association is to provide a forum for coordination and exchange of experiences, by bringing together researchers and professionals working in the Resilience Engineering domain and organizations applying or willing to apply Resilience Engineering principles in their operations. The Resilience Engineering Association held its first General Assembly during the Fourth Symposium, and will in the future play an active role in the organization of symposia and other activities related to Resilience Engineering.