This report presents the results and conclusions from the ambient air monitoring conducted as part of the 2005 Urban Air Toxics Monitoring Program (UATMP)Ca program designed to characterize the magnitude and composition of potentially toxic air pollution in, or near, urban locations. The 2005 UATMP included 47 monitoring stations that collected 24-hour air samples, typically on a 6- or 12-day schedule plus special monitoring in the aftermath of Hurricane Katrina. Forty-six sites analyzed ambient air samples for concentrations of 60 volatile organic compounds (VOC) and/or 15 carbonyl compounds. Thirteen sites also analyzed for 80 speciated nonmethane organic compounds (SNMOC). Six sites analyzed for 19 semivolatile compounds (SVOC) while fifteen sites analyzed 11 metal compounds. Overall, nearly 170,000 ambient air concentrations were measured during the 2005 UATMP. An additional 34,000 ambient air concentrations were added due to Hurricane Katrina sampling. The summary presented in this report uses various graphical, numerical, and statistical analyses to put the vast amount of ambient air monitoring data collected into perspective. Not surprisingly, the ambient air concentrations measured during the program varied significantly from city to city and from season to season. This report describes and interprets these spatial and temporal variations separately for halogenated hydrocarbons, hydrocarbons, polar compounds, and carbonyls. The ambient air monitoring data collected during the 2005 UATMP serve a wide range of purposes. Not only do these data characterize the nature and extent of urban air pollution close to the 47 monitoring stations participating in this study, but they also indicate some trends and patterns that may be common to all urban environments. Therefore, this report presents some results that are specific to particular monitoring locations and presents other results that are apparently common to urban environments. These results should ultimately provide additional insight into the complex nature of urban air pollution. The final data are also included in the appendices to this report.