GULag or Gulág is an acronym for the Russian term Glavnoye Upravleniye ispravitelno-trudovyh Lagerey (Главное Управление Исправительно-трудовых Лагерей), or "Chief Administration of Corrective Labour Camps", the bureaucratic name of the Soviet concentration camp main governing board, and by metonymy, the camp system itself. The original Russian title of the book is "Arkhipelag GULag", the rhyme supporting the underlying metaphor deployed throughout the work. The word archipelago compares the system of labor camps spread across the Soviet Union with a vast "chain of islands", known only to those who were fated to visit them.

Since the Soviet Union's collapse and the formation of the Russian Federation, "The Gulag Archipelago" is included in the high school program in Russia as mandatory reading.

Structurally, the text is made up of seven sections divided (in most printed editions) into three volumes: parts 1–2, parts 3–4, and parts 5–7. At one level, the Gulag Archipelago traces the history of the Soviet concentration camp and forced labour system from 1918 to 1956, starting with V.I. Lenin's original decrees shortly after the October Revolution establishing the legal and practical frame for a slave labor economy, and a punitive concentration camp system. It describes and discusses the waves of purges, assembling the show trials in context of the development of the greater GULag system with particular attention to the legal and bureaucratic development.

The legal and historical narrative ends in 1956, the time of Nikita Khrushchev's Secret Speech at the 20th Party Congress of 1956 denouncing Stalin's personality cult, his autocratic power, and the surveillance that pervaded the Stalin era. Though the speech was not published in the USSR for a long time, it was a break with the most atrocious practices of the concentration camp system; Solzhenitsyn was aware, however, that the outlines of the GULag system had survived and could be revived and expanded by future leaders.

Despite the efforts by Solzhenitsyn and others to confront this Soviet system, the realities of the camps remained taboo into the 1980s. While Khrushchev, the Communist Party, and the Soviet Union's supporters in the West viewed the GULag as a deviation of Stalin, Solzhenitsyn and the opposition tended to view it as a systemic fault of Soviet political culture—an inevitable outcome of the Bolshevik political project. This view, politically unpopular inside and outside the USSR during the Cold War because it ascribed to Lenin the theoretical and practical origins of the concentration camp system, has become the prevalent view of most writers and scholars since the USSR's demise.

Parallel to this historical and legal narrative, Solzhenitsyn follows the typical course of a zek (a slang term for inmate) through the concentration camp system, starting with arrest, show trial and initial internment; transport to the "archipelago"; treatment of prisoners and general living conditions; slave labor gangs and the technical prison camp system (where Andrei Sakharov and his team of prisoner-scientists developed the hydrogen bomb, among other Soviet scientific breakthroughs); camp rebellions and strikes (see Kengir uprising); the practice of internal exile following completion of the original prison sentence; and ultimate (but not guaranteed) release of the prisoner. Along the way, Solzhenitsyn's examination details the trivial and commonplace events of an average zek's life, as well as specific and noteworthy events during the history of the Gulag system, including revolts and uprisings.

Aside from using his experiences as a zek at a scientific prison (a sharashka), the basis of the novel The First Circle (1968), Solzhenitsyn draws from the testimony of 227 fellow zeks, the first-hand accounts which base the work. One chapter of the third volume of the book is written by a prisoner named Georgi Tenno, whose exploits enraptured Solzhenitsyn to the extent that he offered Tenno a position as co-author of the book; Tenno declined.

The sheer volume of firsthand testimony and primary documentation that Solzhenitsyn managed to assemble in The Gulag Archipelago made all subsequent Soviet and KGB attempts to discredit the work useless. Much of the impact of the treatise stems from the closely detailed stories of interrogation routines, prison indignities and (especially in section 3) camp massacres and inhuman practices.

There had been works about the Soviet prison/camp system before, and its existence was known to the Western public since the 1930s. However, never before had the wide reading public been brought face to face with the horrors of the Soviet system in this way. The controversy surrounding this text in particular was largely due to the way Solzhenitsyn definitively and painstakingly laid the theoretical, legal and practical origins of the GULag system at Lenin's feet, not Stalin's. According to Solzhenitsyn's testimony, Stalin merely amplified a concentration camp system that was already in place. This is significant, as many Western Communist or Socialist parties in the seventies tended to view the Soviet concentration camp system as a "Stalinist aberration."

Solzhenitsyn argued that the Soviet government in fact could not govern without the very real threat of imprisonment, and that the Soviet economy depended on the productivity of the forced labor camps, especially in so far as the development and construction of public works and infrastructure were concerned.