The adult correctional population in the United States has been rising steadily since 1980, with nearly 2.4 million people behind bars at any time as of 2007 and another 5 million on some form of probation or parole. All told, 3.2 percent of residents, or 1 in every 31 adults, was under some form of official supervision. These populations are constantly changing: some 700,000 prisoners are released every year from state and federal facilities, and millions pass through local jails every year for short terms. The news media often pay little attention to prison and jail facilities unless there is a disturbance, partly because they can be difficult to access. This is changing somewhat as governments at all levels face budget shortfalls in 2009, which may result in deteriorating conditions and services, as well as early inmate releases. Like other aspects of the criminal justice system, prison and jail practices can vary widely by state and county. The sources listed in this guide can help journalists understand better what is happening behind the walls.