Social Security Disability Insurance (SSD or SSDI) is a payroll tax-funded, federal insurance program of the United States government. It is managed by the Social Security Administration and is designed to provide income supplements to people who are physically restricted in their ability to be employed because of a notable disability, usually a physical disability. SSD can be supplied on either a temporary or permanent basis, usually directly correlated to whether the person's disability is temporary or permanent. Unlike Supplemental Security Income (SSI), SSD does not depend on the income of the disabled individual receiving it. A legitimately disabled person (a finding based on legal and medical justification) of any income level can theoretically receive SSD. ("Disability" under SSDI is measured by a different standard than under the Americans with Disabilities Act.) Most SSI recipients are below an administratively-mandated income threshold, and indeed these individuals must in fact stay below that threshold to continue receiving SSI; but this is not the case with SSD. Informal names for SSDI include Disability Insurance Benefits (DIB) and Title II benefits. These names come from the chapter title of the governing section of the Social Security Act, which came into law in August 1935.

Applicants may hire a lawyer to help them apply or appeal. There are two primary types of organizations: companies with trained specialists experienced in handling SSDI applications and appeals in some or any local community across the country and law firms which specialize in disability-related cases. Most SSDI applicants—about 90 percent according to the SSA—have a disability representative for their appeal. An August 2010 report by the Office of Inspector General for the Social Security Administration indicated that many people submitting an initial disability application for SSDI might benefit from using a third-party disability representative when they first apply for benefits. It indicated that having a disability representative earlier in the process significantly improves the chances of those with four major types of disabilities getting approved for SSDI. The fee that a representative can charge for SSDI representation is set by law. Currently, under the SSA's fee agreement approval process, it is 25 percent of the retroactive dollar amount awarded, not to exceed $6,000. Some representatives may charge fees for costs related to the claim, such as photocopy and medical record collection expenses. If an SSDI applicant is approved quickly and does not receive a retroactive award, the SSA must review and approve the fee a representative will charge the individual. Disability representatives do not charge a fee if they are unsuccessful in obtaining a claimant’s disability benefit. A representative may decline to represent you if, after reviewing your situation, they do not believe you are likely to meet the requirements for SSDI. Most representatives will provide this screening at no cost to you. Typical reasons individuals do not meet the requirements are: their disability is not severe enough or the applicant does not have a sufficient work history (and did not pay enough into FICA - the Federal Insurance Contributions Act