Movies and TV portray hardened criminals cursing God and everyone else.
In reality, many inmates worship God and practice their faith behind bars.
A recent 50-state survey of chaplains offered a rare look at the worshippers behind bars, with the questions asked by the Pew Research Center's Forum on Religion & Public Life in Washington, D.C.
The study said state prisons hold the bulk of the country's convicts (1.4 million), but little has been released to the public on religion in these institutions.
Here are some of the major findings:
ROLE OF CHAPLAINS
Chaplains in state prisons fulfill a range of functions.
Nearly all said they lead worship services, perform religious instruction, do spiritual counseling and organize religious programs. Fifty-seven percent considered the first three their most important functions, but only a third said this is where they spend most of their time.
Thirty-eight percent said most of their time is spent organizing religious programs, and 45 percent said they spend a significant amount of time on paperwork and administrative tasks.
The chaplains are overwhelmingly Christian (mainly Protestant), male and middle-aged. They also are well-educated, with 62 percent having advanced degrees.
And most like their jobs. Two-thirds said they were very satisfied, and only 6 percent were very or somewhat dissatisfied.
"It is rare that a person gets up in the morning and looks forward to going to work, but I do," said Matthew Mason, a chaplain at Crossroads Correctional Center in Cameron, Mo.
REHABILITATION AND RE-ENTRY
If there seems to be one essential, but challenging, aspect of most prison religion programs, it is in the area of rehabilitating inmates and preparing them for re-entry into society.
More than 7 in 10 chaplains considered access to high-quality religion-related programs in prison to be "absolutely critical" to successful rehabilitation and support from religious groups after inmates are released to be absolutely critical to their successful rehabilitation and re-entry.
Fifty-seven percent of chaplains who work in prisons that have rehabilitation or re-entry programs said the quality of the programs have improved in the last three years, and 61 percent said participation has increased.
"I feel that the religious services and programming that are offered here (Crossroads) are of high quality," Mason said. "We have worked very hard to assemble a good group of volunteers who come inside the institution and minister to the offender population."
The study gives considerable attention to the topic of religious extremism in prisons.
The researchers explained: "Since the 9/11 terrorism attacks, religious extremism has been a topic of high public interest in the United States. Some experts specifically have raised concerns that prisons could be a breeding ground for home-grown terrorists and have suggested that prison chaplains and other prison administrators need to monitor religious activity more closely."
Estimates of how common extreme religious views are tend to vary with the security level of the facility and the chaplain's background.