Abstract Water resources sustainability hinges on interre- lated physical, chemical, biological, and human processes, all of which may affect the quantity and quality of available water supplies.California’sdecades-long transition process from intensive and of tenun managed groundwater develop- ment toward more effective, sustainable integrated water resources management has resulted in important lessons. The process offers insights to other countries that seek to achieve sustainability. Long-term systematic groundwater and surface water monitoring programs and ongoing as- sessment of regional groundwater systems are an integral part of management. On local to global scales, the need for fundamental data, regional resources assessments, and increasedsupportforscientificandtechnologicaladvances is becoming increasingly apparent. The scientific commu- nity must enhance society’s understanding of the essen- tial links between basic data needs and the advancement and application of scientific approaches for effective wa- ter management. Correspondingly, scientific and political communitiesmustcoordinatecommoninterestsinendeav- ors toward sustainable management. Public outreach is a necessary complement to achieve sustainability goals and garner support for the programs needed to develop water policies based on sound science, manage water resources, and meet future water demands while avoiding unaccept- able impacts.