We present scientific highlights from the Upper Atmosphere Research Satellite (UARS) pro- gram obtained during the first 5 years of the program. The UARS measures the chemical composition and meteorological state of the middle and upper atmo- sphere as well as the solar irradiance. The comprehen- sive suite of UARS geophysical parameters, their near- global coverage, and the multiyear time span have yielded new insights into the processes affecting our atmosphere. In this article we select seven scientific issues, including stratospheric ozone chemistry, the dy- namics of the middle and upper atmosphere, and solar irradiance variations, and discuss the significant impact that the UARS observations have had on our under- standing of each issue.