A groundwater market is a promising tool for basins implementing California’s Sustainable Groundwater Management Act (SGMA). While the benefits of a cap- and-trade system for both groundwater users and regulators are potentially very large, so too are the risks. Creating a functioning market is not easy. Since 2015, Matthew Fienup has been in the trenches, developing a groundwater market for three coastal basins in Ventura County, California, an area known as Fox Canyon. This presentation will highlight lessons learned during the design and implementation of the Fox Canyon Groundwater Market, the first market to be implemented under SGMA.