Water resource management has become a vital issue in Mongolia. Climate change is affecting the variability of water resources, urbanization in Ulaanbaatar is increasing the demand for water in Mongolia’s capital, and resource extraction and agricultural practices are putting extensive demands and water quality concerns on irregular resources. In response to these challenges, many government institutions, international organizations and non-governmental organizations have come up with a set of recommendations for action. Since the water supply of Ulaanbaatar is dependent on groundwater, the uncertainty around the sustainability and long-term effects of pumping rates, demand growth, and climate impacts are critical to understand. Improved groundwater modeling and monitoring design will enable Mongolia to better inform implementation of Integrated Water Resource Management (IWRM) and reduction of risk from extreme climate events. IWRM integrates the objectives of economic growth, environmental quality, social well-being and financial sustainability in planning and investments. Mongolia has already started implementing IWRM solutions, and the theme carries prominently through its “Water Action Plan” established by the National Water Committee. In particular, multi-objective planning under possible conflicting interests requires including a robust groundwater model into the Shared Vision Planning (SVP)/IWRM decision model to examine trade-offs and prioritize among measures and policies to ensure water security. As Mongolia’s water demands grow, groundwater modeling and IWRM techniques will become even more important to ensure the success and prosperity of the country, reduce water scarcity concerns and provide clean and sustainable resources for future generations. In partnership with the Mongolia Ministry of Environment, Green Development, and Tourism (MEGDT), the U.S. Army Corps of Engineers (USACE), with the support of the U.S. Indo-Pacific Command (USINDOPACOM) and the U.S. Geological Society (USGS), Fresh Water Institute (FWI) and others, assisted the Government of Mongolia with groundwater modeling capacity building. The project supported strategic water security decision-making by developing and improving groundwater models for the Tuul River Basin aquifer, which supplies 98% of the water for Ulaanbaatar, Mongolia. The USGS, in collaboration with USACE, provided groundwater training and capacity building in MODFLOW (3D finite-difference groundwater model) for Mongolia. The training provided understanding of groundwater principles, aquifer characterization, and data acquisition needed to design, construct, and use groundwater models. The second phase of the project included an additional training workshop on more advanced groundwater modeling topics, including sensitivity analysis. It taught participants how to couple the MODFLOW groundwater model with the HEC-RAS surface water model to characterize the groundwater-surface water dynamics. This took model development further toward use in IWRM decision-making and illuminated remaining data gaps.