In recent decades, imprisonment soared in America. Currently, over 2 million people are behind bars. Many people have questioned this trend. They ask, How did it happen, what have been its effects, and how might it be changed? This roundtable will survey a recent report from the National Academy of Sciences on these questions, due for release this month. In 2012, NAS established a Committee on Causes and Consequences of High Rates of Incarceration. It was chaired by Jeremy Travis, president of John Jay College, with Bruce Western, professor of sociology at Harvard, as vice chair. Both are leading figures in criminal justice. The other members included several prominent experts on crime, prison trends, and national social policy. The report attributes the run-up in incarceration initially to tougher punishments for crimes legislated by states since the 1970s. Drawing on a wide literature, it then attributes these changes to increases in crime and other social trends, but also to responses by government and the special features of American politics. Several chapters investigate the concrete effects of growing prisons. One key issue is how much credit rising imprisonment should get for the declines in crime since the 1990s. Another question is the effects, not only on the offenders themselves, but on their families and communities. Finally, the report specifies penal policies that the federal and state governments should reconsider in order to reduce incarceration. The report never overstates what we know, yet its message is still clear: incarceration in America is excessive, and it can and should be reduced. Several states are already revising their prison policies. This report provides the best rationale we have for that movement. As chair, Lawrence Mead of New York University will briefly describe the incarceration problem and introduce the other speakers. Craig Haney, of the University of California at Santa Cruz, will summarize the report’s principal findings. Bruce Western, Harvard University, will discuss the important technical issues raised by the report, including its cautious conclusions about the impact if imprisonment on crime. As discussant, Sarah Lawrence of Stanford Law School will appraise the report, including its relevance to California and other states that are now confronting prison reform. Discussion with the audience will follow. Mead, Haney, and Western were members of the NAS committee, while Lawrence is an expert on criminal justice at the state level, which is the main arena for change. Her recent focus has been on reform in California, our largest state, where reforms have been especially dramatic. The problems of poor men are now the frontier in American antipoverty policy. Too many men are immured in crime and prison. How do we bring them in from the cold? To answer that means tackling incarceration. Given the importance of that problem and this report, this panel could well become a mini-plenary. [468 words]