This report contains a collection of papers presented at a workshop in Merida, Mexico—Strengthening Science-Based Decision Making: Sustainable Management of Groundwater in Mexico. The cross-cutting themes of the workshop were the elements or principles of science-based decision making and the role of the scientific community in ensuring that science is an integral part of the decision making process. Papers included in this volume describe the groundwater resources of Mexico's Yucatan Peninsula, approaches to managing groundwater in Mexico and governmental and scientific institutions concerned with water resources. Other papers discuss US approaches to managing scarce water resources. Participants in the workshop included representatives from leading scientific and academic institutions, federal state and local governments, non-governmental organizations and businesses.