T he Bureau of Prisons (BOP) is the largest correctional agency in the country in terms of the number of prisoners under its jurisdiction. BOP was established in 1930 to house federal inmates, professionalize the prison service, and ensure consistent and centralized administration of the federal prison system. At the end of 1930, BOP operated 14 facilities that held approximately 13,000 inmates. By the end of 1940, BOP had expanded to 24 facilities that held approximately 24,000 inmates. The number of inmates in the federal prison system, with a few fluctuations, remained at approximately 24,000 for the next four decades. Then, beginning in FY1980, the federal prison population started a nearly unabated, three-decade increase. The total number of inmates under BOP's jurisdiction increased from approximately 25,000 in FY1980 to over 205,000 in FY2015. Between FY1980 and FY2013, the federal prison population increased, on average, by approximately 5,900 inmates annually. However, the number of inmates in the federal prison system decreased from FY2013 to FY2015. The U.S. Sentencing Commission (USSC), BOP, and scholars have identified several policy changes over the past three decades that have contributed to the growth of the federal prison population: increases in the number of federal offenses subject to mandatory minimum sentences, changes to the federal criminal code that have made more crimes federal offenses, and the elimination of parole. There are a number of policy avenues lawmakers could consider should Congress choose to address the growth in the federal prison population. Several options—such as expanding the capacity of the federal prison system, continued investment in rehabilitative programs, and placing inmates in private prisons—either continue or expand current correctional policies. However, Congress might also consider changing some existing correctional or sentencing policies as a means of addressing some of the issues related to the growth of the federal prison population. Some of these options include placing some inmates in alternatives to incarceration, such as probation, or expanding early release options by allowing inmates to earn more good time credit or allowing inmates to be placed on parole once again. Congress could consider reducing the amount of time inmates are incarcerated in federal prisons by repealing mandatory minimum penalties for certain offenses or reducing the length of the mandatory minimum sentence. Finally, policymakers could consider repealing federal criminal statutes for some offenses. Congress is currently considering legislation that would put into effect some of the policy options discussed in this report, including expanding the "safety valve" for some low-level offenders, allowing inmates to earn additional good time credit as a part of a risk and needs assessment system, and reducing mandatory minimum penalties for some offenses. The Government Accountability Office (GAO) reported that BOP faces several challenges resulting from the increasing number of inmates placed under its supervision. According to GAO, BOP reported increased use of double and triple bunking, which brings together for longer periods of time inmates with a higher risk of violence and more potential victims; waiting lists for education and drug treatment programs, which can pose a threat to institutional security by increasing inmate idleness and may decrease recidivism-reducing benefits these programs can provide; limited meaningful work opportunities, which can also contribute to inmate idleness; crowded visiting rooms, which can make it difficult for inmates to visit with their families; and increased inmate-to-staff ratios, which can compromise institutional safety by increasing staff overtime and stress while reducing staff-inmate communication. GAO also noted that the growing federal prison population is taxing BOP's infrastructure, which was designed to manage a smaller prison population. BOP is also facing increasing maintenance costs as older facilities age. The burgeoning prison population has contributed to mounting operational expenditures for the federal prison system. BOP's appropriations increased more than $7.1 billion from FY1980 ($330 million) to FY2016 ($7.479 billion). BOP's expanding budget is starting to consume a larger share of the Department of Justice's (DOJ) overall annual appropriations, meaning that funding for the federal prison system might start to crowd out funding for other DOJ initiatives. In FY1980 appropriations for BOP accounted for 15% of the total amount appropriated for DOJ; in FY2016 it was 26%. The growth in the federal prison population over the past three decades has resulted in an increasingly expensive federal prison system that is overcrowded and aging and where facilities might not be staffed at an optimal level. Congress could choose to address the mounting number of federal inmates either in the context of existing correctional policies or by changing the current policies. Under the umbrella of continuing existing policies, Congress could consider addressing issues related to the burgeoning federal prison population by (1) expanding the capacity of the federal prison system, (2) continuing to invest in rehabilitative programming, (3) placing more inmates in private correctional facilities, or some combination of the three. Arguably one of the most straightforward approaches for managing the steadily increasing number of federal inmates is to expand the capacity of the federal prison system. Congress could choose to mitigate some issues related to federal prison population growth by appropriating more funding so BOP could expand prison capacity to alleviate overcrowding, update and properly maintain existing facilities, and hire additional staff. While a large-scale expansion of the federal prison system might help reduce overcrowding, it takes several years for a prison to be built and be ready to accept inmates. If Congress chooses to appropriate funding for an expansion of BOP's infrastructure, it could be several years before overcrowding is reduced. There may be some concern that Congress might invest a significant amount of funding in expanding BOP's capacity and then the prison population will drop. The number of federal inmates has decreased in each of the past two fiscal years (see Table A-1 ). Even so, the federal prison system is still operating at 23% over capacity. Should Congress choose to invest in a wide-scale expansion of prison capacity, and the prison population decreases in the future, the surplus bedspace could allow BOP to close some of its older facilities. Expanding prison capacity would generally require more maintenance and need higher staff-to-inmate ratios to safely operate. Critics contend that expanding the capacity of the federal prison system does not address the growth of the federal prison population since the early 1980s. Also, this policy option would not resolve the issue of the rising cost of the federal prison system; in fact, it could exacerbate it. However, alternatives that would reduce the federal prison population would most likely involve prosecuting fewer people in federal courts, providing ways for inmates to be released before they served a significant portion of their sentences, putting more inmates into diversionary programs, or placing more offenders on some form of community supervision. If Congress does not seek to take any of these steps, a large-scale expansion of the federal prison system might be the sole way to manage the effects of an increasing prison population. Some may argue that in order to protect public safety Congress should appropriate the funding necessary to expand the federal prison system rather than adopt policy changes that would reduce the prison population through early releases, alternatives to incarceration, or fewer prosecutions. A review of the literature on rehabilitative programs (e.g., academic and vocational education, cognitive-behavioral programs, and both community- and prison-based drug treatment) suggests that there are enough scientifically sound evaluations to conclude that these programs are effective at reducing recidivism, which could potentially help stem growth in the federal prison population in the future. BOP offers a variety of rehabilitation programs such as academic and vocational education, work programs through the Federal Prison Industries (FPI), substance abuse treatment, and cognitive-behavioral programs that focus on promoting pro-social behavior. One possible option for reducing the federal prison population would be to ensure that BOP has adequate resources to provide rehabilitative services to inmates. At a time when some policymakers are considering reducing discretionary funding for federal agencies, there might be some effort to restrain the growth of BOP's appropriations, including for rehabilitative services. BOP has to administer the federal prison system within the funds appropriated for it by Congress. If BOP does not have sufficient resources, it might not be able to provide rehabilitative programming to all inmates who need it. It could be argued that in order to reduce the growing cost of operating the federal prison system, BOP should reduce funding for rehabilitative programming and invest solely in providing for the subsistence of inmates and maintaining a level of staffing that is adequate to ensure that federal prisons are secure. However, reducing programming opportunities might result in more inmate idleness, which might in turn result in more inmate misconduct. Moreover, BOP is authorized to reduce an inmate's sentence by up to one year for successfully completing a residential substance abuse treatment program; therefore, reducing programming opportunities could hamper one of the few avenues BOP has for releasing inmates early. It is also possible that BOP might be able to realize some long-term cost savings by successfully rehabilitating inmates. For example, research by the Washington State Institute for Public Policy (WSIPP) suggests that effective rehabilitation programs can result in cost savings. As policymakers consider the appropriate level of funding for BOP in light of concerns about the federal deficit and potential freezes or reductions in non-defense discretionary spending, they may consider whether it is prudent to increase resources for BOP's rehabilitative programs in the near term in order to realize potential long-term benefits. The size of the effect that decreased recidivism among federal offenders would have on BOP's budget would depend on how many new inmates BOP incarcerates. If new commitments exceed the number of inmates released who do not return to prison, then the demand for prisons, personnel, and inmate programs and services would continue to grow, although possibly at a slower rate.