This article is a guide to the NBER-Rensselaer Scientific Papers Database, which includes more than 2.5 million scientific publications and over 21 million citations to those papers. The data cover an important sample of 110 top U.S. universities and 200 top U.S.-based R&D-performing firms during the period 1981-1999. This article describes the file system which comprises the database, explains the variables included in the files, and discusses the functions of the various files. It includes numerous descriptive tables, as well as graphs of the data in the time series dimension. In addition, it discusses limitations and strengths of the data as well as some questions that the data might be used to address.