This report provides a record of lifeline performance during the two most damaging U.S. earthquakes at the start of 21st century. Information is provided on current seismic practice, on the seismic resistance and vulnerability of different infrastructure, and on the present understanding of engineers who design roads, bridges, pipelines, and power systems. This monograph will be useful to researchers, practicing engineers, and administrators interested in the repercussions of building lifelines near earthquake faults, on seasonally frozen soils, on loose sands and alluvium, and in regions with complex or unknown seismicity. The Earthquake Investigations Committee of the Technical Council of Lifeline Earthquake engineering (TCLEE), American Society of Civil Engineers (ASCE) was established to initiate, organize, train for, coordinate, and evaluate the performance of lifelines following earthquakes. It includes topics on the San Simeon Earthquake: Seismology and Geotechnical Issues; Communications; Dams; Power Systems; Gas and Liquid Fuel; Highways and Bridges; Airports and Ports; Railroads; Water Systems; Wastewater Systems; and Emergency Response. Topics on the Denali Earthquake: Seismology and Geotechnical Issues; Highway System; Trans-Alaska Pipeline System (TAPS); Airports; Water and Wastewater; Communications; Railways; and Electric Power.