The Social Security Death Index (SSDI) was a database of death records created from the United States Social Security Administration's Death Master File until 2014. Since 2014, public access to the updated Death Master File has been via the Limited Access Death Master File certification program instituted under Title 15 Part 1110. Most persons who have died since 1936 who had a Social Security Number (SSN) and whose death has been reported to the Social Security Administration are listed in the SSDI. For most years since 1973, the SSDI includes 93 percent to 96 percent of deaths of individuals aged 65 or older. It was frequently updated; the version of June 22, 2011 contained 89,835,920 records.

Unlike the Death Master File, the SSDI is available to the public at many online genealogy websites. The SSDI is a popular tool for genealogists and biographers because it contains valuable genealogical data. It is also useful for medical research such as clinical trials and epidemiology, because where survival data is missing from medical records (for reasons such as loss to follow-up), the SSDI can be used to backfill it.