Introduction Jails play a unique role in our criminal justice system. For many, jail is the point of entry into the criminal justice system ( Irwin, 1985 ). While the importance of jails is unquestioned, the jail is often the most misunderstood of the agencies that make up the criminal justice system. This chapter takes a look at this unique institution within the criminal justice system, first exploring the history, both in England and in the United States, and then addressing concerns with modern jail facilities and their management and operation. To begin this journey, let us first define what a jail is and, for that matter, what it is not.