Although the problem of mass incarceration in America’s state prisons is well known, rapid jail growth at the local level is not. There are approximately 3,000 jails in the United States, with more than 11 million admissions each year. Jails touch the lives of many more people than prisons, and their growth, use, and management are vital areas of concern for local governments. The purpose of jails is to hold people who pose a risk of flight or of reoffending while their criminal case is pending. In reality, however, jails hold many people who are low-risk for flight or reoffending. Rather, they are simply too poor to pay even low bail amounts, or they have complex mental health or substance abuse needs that localities lack the resources to address. As a result, many jails in America house people who don’t need to be there. Reversing the misuse of jails is a critical goal in ending mass incarceration and making America a more just and equal country.