As a hydrogeologist and hydrologist, my research involves the study of water resources and water security with emphasis on freshwater. Using lab and field data, our aim is to develop an understanding of fundamental aspects of the transport of water and contaminants, and to investigate regional water resources systems. We have developed simulation-based planning tools to aid in sustainable agricultural and urban water management in the US, Mexico, India, and Jordan. With my colleagues, we have initiated the Global Freshwater Initiative, which studies water resources vulnerability problems throughout the world. During the past 15 years, our field investigations have focused on the interactions between groundwater and patterns of vegetation in studies of both meadow and salt-marsh ecohydrology. Scales of physical processes of interest extend from the domain of small pores to vast regional subsurface flow environments. Although driven by observations and data, we develop conceptual and quantitative models to rigorously understand physical processes, make predictions, and explore the impacts of new water management policies, such as taxes, quota, and markets. Such models enhance our understanding of groundwater flow behavior and provide the means to better manage water resources.