Following on the promising findings from HOPE probation in Hawaii—that swift and certain, but modest sanctions in response to technical probation violations reduced recidivism and drug use—in 2012 the US Department of Justice launched a Demonstration Field Experiment (DFE) of HOPE in four mainland jurisdictions. The intent of the DFE is for each site to adhere as closely as possible to the HOPE principles, with accommodations as necessary to local circumstances. Each site has presented different challenges to implementation that suggest that the success of a HOPE-style program may require more than a simple commitment to adopting the HOPE principles and to providing the necessary resources. These challenges include differences in state legal codes, local and state institutional structures, political environments, and geography and demographics. This presentation will describe: (1) the differences among the sites that bear on implementation, (2) how those differences have been accommodated, (3) how they might affect outcomes, and (4) how this experience might generalize to other DFEs of promising criminal-justice reforms.