The High Resolution Dynamics Limb Sounder (HIRDLS) has been built to provide data with unprecedented detail on the structure and composition of the Middle Atmosphere, with particular emphasis on the region around the tropopause. Scheduled to be launched on the EOS Aura platform, HIRDLS will measure temperature, H₂O, O₃, N₂O, NO₂, N₂O₅, HNO₃, CF₂Cl₂, CFCl₃, CLONO₂, CH₄, and aerosols. These measurements will be made with a longitudinal and longitudinal resolution of < 5 ^o and vertical resolution of 1 km, from ~ 7 to 80 km. Updated estimates of performance will be presented, based on calibration data. Most of the time will be spent discussing how such measurements will be used to provide improved insight into atmospheric problems.