This report contains a valuable summary of state-of-the-art groundwater monitoring network designs and was prepared for the needs of analysts and practitioners. The Task Committee on Long-Term Groundwater Monitoring of EWRI/ASCE has reviewed the methods for the design of groundwater monitoring networks. The methods consist of analytical and quantitative procedures that identify optimal sampling locations and times to obtain representative groundwater quality data essential in the development of groundwater management strategies. Included are several chapters that address: The Objectives of Long-Term Groundwater Monitoring, Data Requirements in Groundwater Monitoring Network Design, Case Studies, and Future Research and Technology Transfer Needs in Groundwater Hydrology and Hydrogeology. Those involved in groundwater practice and management will find detailed descriptions of the leading methodologies for groundwater monitoring network designs and guidance for the implementation in a variety of field conditions.