This paper describes and analyzes the results of the Third Message Understanding Conference (MUC-3). It reviews the purpose, history, and methodology of the conference, summarizes the participating systems, discusses issues of measuring system effectiveness, describes the linguistic phenomena tests, and provides a critical look at the evaluation in terms of the lessons learned. One of the common problems with evaluations is that the statistical significance of the results is unknown. In the discussion of system performance, the statistical significance of the evaluation results is reported and the use of approximate randomization to calculate the statistical significance of the results of MUC-3 is described