The SAS™ system is a programming and data analysis package developed and sold by SAS Institute, Cary, North Carolina. SAS markets many products; when installed together they result in an integrated environment. In this book we address software available in the Base SAS, SAS/STAT, SAS/GRAPH, SAS/ETS, and SAS/IML products. Base SAS provides a wide range of data management and analysis tools, while SAS/STAT and SAS/GRAPH provide support for more sophisticated statistical methods and graphics, respectively. We touch briefly on the IML (interactive matrix language) module, which provides extensive matrix functions and manipulation, and the ETS (Econometrics and Time Series) module, which supports time series tools and other specialized procedures.