**Preface to "Advances in Transboundary Aquifer Assessment"**

Groundwater as a resource is being increasingly relied on globally to serve emerging and developing water needs. Characterizing groundwater aquifer systems in terms of geology and groundwater quality, quantity, and sustainability is critical to understanding the physical and socioeconomic implications of its use. Of special consideration is aquifer assessment in a transboundary setting, where the cooperation of multiple jurisdictions, sometimes with different languages and cultures, is required. This Special Issue features studies of transboundary aquifers, particularly at the border shared by Mexico and the United States, a semi-arid to arid region experiencing significant population growth and changing climate conditions. The papers represent a broad array of investigations of complex physical aquifer systems and related institutional settings, including the identification and prioritization of the needs and strategies for sustainable groundwater development and use; the characterization of the physical framework of the aquifer, stressors on the aquifer system, and how those stressors influence the availability of groundwater in terms of its quantity and quality; and the incorporation of stakeholder input and prioritization directly into the process of aquifer assessment and model building. We hope that this collection of diverse papers provides useful information and encourages additional research that contributes to understanding groundwater and aquifer systems.

> **Sharon B. Megdal and Anne-Marie Matherne** *Editors*
