The 2012 Great Lakes Water Quality Agreement includes a commitment to publish a report on relevant and available groundwater science. In response to this commitment, a report that documents groundwater science relevant to the Great Lakes Water Quality Agreement has been finalized after considering public comments received over December 2015 to the end of January 2016. The report is a product of extensive collaboration among experts in a variety of subject areas and summarizes current knowledge on groundwater in the Great Lakes region. This effort was led by the Groundwater Annex Subcommittee.