SSDI (Social Security Disability Insurance) is for people who have worked and paid Social Security taxes but are no longer able to work because of a qualifying disability. Eligibility is based on your work history and earned work credits.
SSI (Supplemental Security Income) is a needs-based program for individuals with limited income and resources who are disabled, blind, or age 65 or older. Unlike SSDI, SSI does not require a qualifying work history.