This report documents ModelMate, a graphical user interface for model analysis. The documentation presented herein describes installation and use of the application. The perfor- mance of ModelMate has been successfully tested in a variety of modeling and model-analysis scenarios. If, however, errors are detected in this document or in the functioning of the program, users are requested to notify the U.S. Geological Survey. Updates might occasionally be made to this document and to the program. Users can download the software and check for updates on the Internet at http: //water.usgs.gov/software/ModelMate/