First referenced in Article I, Section 10, Clause 3 of the United States Constitution, interstate compacts are the most formal mechanism available to policymakers seeking state-driven solutions to a wide range of policy challenges. Of all the tools available to state policymakers trying to work cooperatively across borders, interstate compacts are the most formal and perhaps the least understood.1 Compacts hold a unique place in American history for several different reasons. First, while the use of interstate compacts dates back to the founding of the country, the frequency with which they are used has expanded considerably over the last half century. Second, compacts provide state policymakers with a sustainable tool capable of promoting interstate cooperation without federal intervention. Third, interstate compacts can be used to address a wide range of policy challenges, ranging from insurance reform to environmental regulation and virtually everything in between.