This Proceedings presents 107 state-of-the-art reports and results of studies by investigators who have analyzed and evaluated the effects of natural and technological hazards on lifelines. New research has been conducted on the seismic performance of lifelines, new standards and codes have been developed, and major lifeline projects have been rehabilitated, designed, and constructed. The lifeline performance of the Trans-Alaska Pipeline during the November 3, 2002, Denali Fault earthquake demonstrates how lifelines properly designed and constructed for severe earthquake ground motions can perform well. The Sixth U.S. Conference and Workshop on Lifeline Earthquake Engineering (TCLEE 2003) was held in Long Beach, California, on the 10th anniversary year of the 1993 Long Beach earthquake. The theme for TCLEE 2003: Advancing Mitigation Technologies and Disaster Response highlighted the need to focus all efforts on natural and technological hazards. Topics include: Lifeline Management and Policy Issues; Transportation System Preparedness, Response, and Recovery; Retrofit and Policy Issues with the Bay Area Rapid Transit (BART) System; Post-Earthquake Investigations and Lifeline Performance During Earthquakes; Lifeline Guides and Codes; Performance of Ports and Wharves; Water and Waste Water Systems and Components; The Trans-Alaska Pipeline and the 2002 Denali Fault Earthquake; Electric Power Guidelines and Performance of Equipment; Design, Mitigation, and Performance of Underground Pipelines; Seismic Hazard and Risk Issues; Seismic Risk Analysis of Highway Systems; Geotechnical Lifeline Issues; and Innovative Mitigation of Bridges.