Concern among some Members of Congress and the public over the financial sustainability of the Social Security Disability Insurance (SSDI) program has grown. Under current law, the Federal Disability Insurance (DI) Trust Fund—which finances the benefits and administrative costs of the SSDI program—is projected to be exhausted by the fourth quarter of calendar year 2016. If depleted, the DI trust fund would be able to pay about 80% of scheduled SSDI benefits. The declining solvency of the DI trust fund is the result of an increasing imbalance between SSDI's income and outlays. Between 1980 and 2013, non-interest income to the DI trust fund (adjusted for inflation) increased 181%, while spending on benefits grew 219%. The increase in spending is due largely to the growth in the number of beneficiaries on SSDI. Over the same period, the number of disabled workers and their dependents more than doubled, rising from 4.7 million in 1980 to 11 million in 2013. Because benefit payments account for nearly all program spending, the growth in the SSDI rolls has contributed heavily to the financial difficulties of the DI trust fund. To assist lawmakers in addressing the sustainability of the program, this report provides an overview of reform proposals to manage the long-term growth in the SSDI rolls. The report is divided into four sections. The first section provides a brief background on SSDI, including program eligibility criteria, benefits, and the initial determination and adjudication process. The second section discusses the growth in the SSDI rolls since 1980 by examining historical entry and exit trends in the program. The third section investigates some of the causes of growth in SSDI, including changes in the demographic characteristics of the working-age population, changes in opportunities for work and compensation, and changes in federal policy. The fourth section examines various options to manage the growth in the SSDI rolls, namely, (1) stricter eligibility criteria, (2) improved administration of the program, (3) stronger return-to-work incentives, and (4) policies to encourage employers to help disabled workers continue to work. Many of the options discussed in this report could reduce spending by slowing or even reducing the growth of SSDI over the long term; however, such options are unlikely to produce savings in time to prevent the projected exhaustion of the DI trust fund in 2016. For information on financing options to extend the solvency of the DI trust fund in the short term, see CRS Report R43318, Social Security Disability Insurance (DI) Trust Fund: Background and Solvency Issues , by [author name scrubbed]. Enacted in 1956 under Title II of the Social Security Act, SSDI is part of the Old-Age, Survivors, and Disability Insurance (OASDI) program administered by the Social Security Administration (SSA). OASDI is commonly called Social Security. Like Old-Age and Survivors Insurance (OASI), SSDI is a form of social insurance that replaces a portion of a worker's earnings based on the individual's career-average earnings in jobs covered by Social Security. Specifically, SSDI provides benefits to insured workers under the full retirement age (FRA) who meet the statutory test of disability and to their eligible dependents. FRA is the age at which unreduced Social Security retirement benefits are first payable (currently 66). In November 2014, 10.9 million individuals received SSDI benefits, including 9 million disabled workers, 150,000 spouses of disabled workers, and 1.8 million children of disabled workers. To qualify for SSDI, workers must be (1) insured in the event of disability, and (2) statutorily disabled. To achieve insured status, individuals must have worked in covered employment (i.e., jobs covered by Social Security) for about a quarter of their adult lives before they became disabled and for at least five of the past 10 years immediately before the onset of disability. However, younger workers may qualify with less work experience based on their age. In 2014, SSDI provided disability insurance to an estimated 151 million workers. To meet the statutory test of disability, insured workers must be unable to engage in any substantial gainful activity (SGA) because of a medically determinable physical or mental impairment that can be expected to result in death or has lasted or can be expected to last for at least one year. In 2015, the monthly SGA earnings limit is $1,090 for most workers and $1,820 for statutorily blind individuals. In general, workers must have a severe condition that prevents them from doing any kind of substantial work that exists in the national economy, taking into account age, education, and work experience. Cash benefits begin five full months after a beneficiary's disability onset date. Initial benefits are based on a worker's career-average earnings, indexed to reflect changes in national wage levels (up to five years of the worker's low earnings are excluded). Benefits are subsequently adjusted to account for inflation through cost-of-living adjustments (COLA), as measured by the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W). However, benefits may be offset if a disabled worker also receives workers' compensation or other public disability benefits. In November 2014, the average monthly benefit was $1,146 for disabled workers, $309 for spouses of disabled workers, and $343 for children of disabled workers. In addition to cash benefits, disabled workers and certain dependents are eligible for health coverage under Medicare after 24 months of entitlement to cash benefits (29 months after the onset of disability). In 2012, Medicare spending per disabled beneficiary averaged about $9,900. Some SSDI beneficiaries may also qualify for Supplemental Security Income (SSI). SSI provides cash payments to aged, blind, or disabled individuals with limited income and assets. Both programs are administered by SSA and use the same definition of disability; however, unlike SSDI, SSI has no work or contribution requirements. In most states, SSI recipients are automatically eligible for Medicaid. Over 1 million disabled workers ages 18-64 received both SSDI and SSI benefits in December 2013. To apply for SSDI, an individual must first file an application with a local SSA field office. Applications that meet the work history and earnings requirements are then forwarded to a state Disability Determination Services (DDS) office for a medical determination. DDSs—state agencies that are fully funded by the federal government—decide whether applicants meet national disability standards established by SSA. State DDS examiners and medical and psychological consultants typically use medical evidence collected from the claimant's treating sources (physicians, psychologists, or other acceptable medical sources) to determine the severity of the claimant's impairment(s). If a claimant's condition is determined to be severe and meets (or is of equal severity to) the medical criteria in SSA's Listing of Impairments , the claimant is considered disabled and therefore eligible for SSDI. Claimants who do not meet the medical criteria in the listings proceed to a more individualized assessment that examines their residual functional capacity to perform any past relevant work or other work that exists in the national economy. If a claimant cannot perform such work, the claimant is awarded benefits. Claimants whose initial applications are denied may appeal. During the appeals process, claimants may present additional evidence or arguments to support their case as well as appoint a representative to act on their behalf. The appeals process is composed of four stages: (1) reconsideration by a different examiner from the state DDS office, (2) a hearing before an administrative law judge (ALJ), (3) a review before the Appeals Council, and (4) filing suit against SSA in U.S. district court. Almost all appeals reach the ALJ stage; few proceed to the Appeals Council or federal court. Between 1980 and 2013, the number of SSDI applications submitted to SSA's field offices doubled, from 1.3 million to 2.6 million. As Figure 1 illustrates, most of that growth began around 2000. The number of awards for SSDI increased 111% over this same period, from 420,000 in 1980 to 888,000 in 2013. At the same time, the overall incidence (enrollment) rate rose from 4.4 awards per 1,000 disability-exposed to 6.3. The incidence rate is the ratio of the number of new beneficiaries awarded benefits each year to the number of workers who are insured in the event of disability but not currently receiving benefits (i.e., the disability-exposed population ). Entitlement to benefits ends when a disabled worker no longer meets the eligibility criteria for SSDI. Although the overall number of disabled-worker terminations increased 77% between 1980 and 2013, from 435,000 to 769,000, the ratio of annual disabled-worker terminations to the average number of disabled-worker beneficiaries (the termination rate ) actually decreased 41%, from 145 disabled-worker terminations per 1,000 disabled-worker beneficiaries to 86. As depicted in Figure 2 , three main factors drive the termination rate: death, recovery, and conversion. The beneficiary death rate decreased 42% between 1980 and 2013, from 48 disabled-worker terminations per 1,000 disabled-worker beneficiaries to 28, reflecting the trend in the U.S. population of declining mortality rates across all age groups. Recovery refers to individuals whose benefits were terminated because of medical improvement or earnings above SGA. From 1980 to 2013, the recovery rate declined 77%, from 29 disabled-worker terminations per 1,000 disabled-worker beneficiaries to 6.7. A conversion termination occurs when SSA automatically converts a disabled-worker benefit to a retired-worker benefit due to a disabled worker reaching the FRA. Over this same period, the conversion rate fell 25%, from 68 disabled-worker terminations per 1,000 disabled-worker beneficiaries to 51.