As the largest sectoral user of water globally, agriculture is both impacted by and a major driver of water scarcity. Monitoring of agricultural water use is essential to identify and design effective strategies for balancing water demands with those of other sectors and the environment amidst future changes. Yet most countries face large gaps in their ability to identify where, when, how much and for what purposes water is withdrawn or abstracted by farmers. This chapter provides a critical review of the current evidence about the technical, financial, social and political barriers to effective monitoring of agricultural water use, focusing on the twin challenges of abstraction permitting and water use quantification. We identify enablers and barriers for new technologies – specifically satellite remote sensing – to plug gaps in in situ monitoring infrastructure, and the need to think beyond improved data collection to how such data are then used in design and enforcement of agricultural water resources management and planning policies.