This paper introduces and documents the new Longitudinal Enterprise and Establishment Microdata (LEEM) database, which has been constructed by Census' Economic Planning and Coordination Division under contract to the Office of Advocacy of the U.S. Small Business Administration. The LEEM links three years (1990, 1994, and 1995) of basic data for each private sector establishment with payroll in any of those years, along with data on the firm to which the establishment belongs each year. The LEEM data will facilitate both broader and more detailed analysis of patterns of job creation and destruction in the U.S., as well as research on the structure and dynamics of U.S. businesses. This paper provides documentation of the construction of LEEM data, summary data on most variables in the database, comparisons of the annual data with that of the nearly identical County Business Patterns, and distributions of establishments and their employment by the size of their firms. This is followed by a simple analysis of changes over time in the attributes of surviving establishments, and a brief discussion of turnover (business births and deaths) in the population and gross changes in employment associated with both establishment turnover and with surviving establishments. It concludes with a summary of the strengths and weaknesses of the LEEM.