The special collection on Civil Infrastructures under Extreme Environments is available in the ASCE Library (https://ascelibrary.org /page/jaeeez/under_extreme_environments).Civil infrastructures could experience extreme environments during their life cycles, threatening their safety, serviceability, functionality, and sustainability. Current state-of-the-art engineering practices and research frontiers for terrestrial civil infrastructures under extreme environments could provide valuable background knowledge that will enhance the designs of aerospace structures and extraterrestrial structures and aid in the creation of suitable built environments for human habitation. In assessing civil infrastructures under extreme environments, engineers face challenges in quantifying structural performances for their safety and resilience.This special collection synthesizes the state of the art in the areas of design, analysis, monitoring, construction, and rehabilitation of civil infrastructures under extreme environments. It includes stateof-the-art knowledge and expertise from researchers, engineers, operators, and owners to help understand and quantify the performance of civil infrastructures exposed to extreme terrestrial environments during their life cycles. This special collection includes 12 articles, received in response to a related call for papers published online between March 2019 and August 2020. In general, the included papers offer a diverse, international perspective from research groups around the world. The papers cover a broad range of topics that can generally be grouped into three subject areas: performance assessment of infrastructures in extreme conditions; reliability and cost analysis of infrastructures in extreme conditions; and experimental study of infrastructures in extreme conditions.On the subject of performance assessment of infrastructures, Hou et al. (2019) proposed a new simulation methodology of the traffic performance of partially blocked roadway and bridge links due to hazardous events in their paper "Traffic performance assessment methodology of degraded roadway links following hazards." In their paper "Extreme response of a sea-crossing bridge tower under correlated wind and waves," Fang et al. (2019) evaluated the dynamic responses of bridge towers under the correlated wind and wave loading conditions. Also investigating long-span bridges, Liu et al. (2020) evaluated the wind turbulence intensity effects on the fatigue damage accumulations of long-span bridges in their paper "Stress-level buffeting analysis and wind turbulence intensity effects on fatigue damage of long-span bridges." In their paper "Hybrid nonlinear seismic analysis of bridges with moving traffic," Chen et al. (2020) proposed a hybrid simulation approach to conduct nonlinear seismic analyses of bridge-traffic-earthquake systems. In their paper "Typhoon-induced wind pressure characteristics on large terminal roof based on mesoscale and microscale © ASCE 02021001-2 J. Aerosp. Eng.