Alger Hiss (November 11, 1904 – November 15, 1996) was an American government official accused in 1948 of having spied for the Soviet Union in the 1930s. Statutes of limitations had expired for espionage, but he was convicted of perjury in connection with this charge in 1950. Before the trial Hiss was involved in the establishment of the United Nations, both as a U.S. State Department official and as a U.N. official. In later life he worked as a lecturer and author.

On August 3, 1948, Whittaker Chambers, a former U.S. Communist Party member, testified under subpoena before the House Un-American Activities Committee (HUAC) that Hiss had secretly been a communist while in federal service. Hiss categorically denied the charge and subsequently sued Chambers for libel. During the pretrial discovery process of the libel case, Chambers produced new evidence allegedly indicating that he and Hiss had been involved in espionage. A federal grand jury indicted Hiss on two counts of perjury. After a mistrial due to a hung jury, Hiss was tried a second time, and in January 1950, he was found guilty and received two concurrent five-year sentences, of which he eventually served three and a half years.

Arguments about the case and the validity of the verdict took center stage in broader debates about the Cold War, McCarthyism, and the extent of Soviet espionage in the United States.

Since Hiss' conviction, statements by involved parties and newly exposed evidence have added to the dispute. In the 1990s, two former senior Soviet military officers responsible for the Soviet Union's military intelligence archives stated, following a search of those archives, that the "Russian intelligence service has no documents proving that Alger Hiss cooperated with our service somewhere or anywhere," and that Hiss "never had any relationship with Soviet intelligence." The 1995 Venona Papers prompted more support for the theory that he was a Soviet spy, but were not yet deemed conclusive by many sources. Author Anthony Summers argued in 2000 that since many relevant files continue to be unavailable, the Hiss controversy will continue to be debated. Columnist George Will asserted in Newsweek, “the myth of Hiss’s innocence suffers the death of a thousand cuts.” Hiss maintained his innocence until his death.