An overview of the ARM/FIRE Water Vapor Experiment (AFWEX) is given. This field experiment was conducted during November-December 2000 in the vicinity of the central ground-based ARM site in north central Oklahoma, and was sponsored jointly by the Atmospheric Radiation Measurement, the NASA First ISCCP Regional Experiment, and the National Polar-orbiting Operational Environmental Satellite System programs. Its primary goal was to collect accurate measurements of upper level (~8 to 12 km) water vapor in the vicinity of the ground based ARM site. These data will be used to determine the accuracy of measurements that are made regularly from the ARM site. Relevant scientific interests include the effect of upper level water vapor on outgoing longwave radiation, the formation of cirrus clouds, and validation of operational satellite-based products. The experiment included in-situ, active, and passive sensors aboard two high altitude aircraft that flew over the heavily instrumented ground-based ARM site. This poster describes the motivation and basic goals of the project, the experimental design, atmospheric conditions encountered during the experiment, and some preliminary findings.