In the dystopian novel Nineteen Eighty-Four, thoughtcrime is the offense of thinking in ways not approved by the ruling Ingsoc party. In the official language of Newspeak, the word crimethink describes the intellectual actions of a person who entertains and holds politically unacceptable thoughts; thus the government of The Party controls the speech, the actions, and the thoughts of the citizens of Oceania.

In the story of Nineteen Eighty-Four, the Thinkpol (Thought Police) are responsible for the detection and elimination of thoughtcrime, and for the social control of the populations of Oceania, by way of audio-visual surveillance and offender profiling. Such psychological monitoring allows the Thought Police to detect, arrest, and kill thought criminals, citizens whose independence (intellectual, mental, and moral) challenges the political orthodoxy of Ingsoc (English Socialism) and thus the legitimate government authority of the Party. In the detection of thoughtcrime—and to overcome the physical impossibility of simultaneously policing every citizen of Oceania—the Thinkpol spy upon the populace through ubiquitous two-way telescreens, and so can monitor any person's body language, reflexive speech, and facial expressions:

Any sound that Winston made, above the level of a very low whisper, would be picked up by the telescreen; moreover, so long as he remained within the field of vision which the metal plaque commanded, he could be seen as well as heard. There was, of course, no way of knowing whether you were being watched at any given moment. How often, or on what system, the Thought Police plugged in on any individual wire was guesswork.

— Part I, Chapter 1, Nineteen Eighty-Four

The universal, physical presence of the telescreen, in public and in private spaces, exerted psychological pressure upon each citizen of Oceania to presume that they were under constant Thinkpol surveillance, and thus in danger of detection and arrest as a thought criminal; thus, whenever near a telescreen, Winston Smith was always mindful of that possibility: "If you made unexpected movements, they yelled at you from the telescreen." Such surveillance methods allowed the Thinkpol and the Ministry of Love (Miniluv) to become universally feared by the citizens of Oceania, especially by the members of the Outer Party, which includes Winston Smith.

In the Newspeak vocabulary, the word crimestop denotes the citizen's instinctive desire to rid himself of unwanted, incorrect thoughts (personal and political), the discovery of which, by the Thinkpol, would lead to detection and arrest, transport to and interrogation at Miniluv (Ministry of Love). The protagonist, Winston Smith, describes crimestop as a conscious process of self-imposed cognitive dissonance:

The mind should develop a blind spot whenever a dangerous thought presented itself. The process should be automatic, instinctive. Crimestop, they called it in Newspeak. ... He set to work to exercise himself in crimestop. He presented himself with propositions—'the Party says the Earth is flat', 'the Party says that ice is heavier than water'—and trained himself in not seeing or not understanding the arguments that contradicted them.

Moreover, from the perspective of Oceania's principal enemy of the state, in the history book The Theory and Practice of Oligarchical Collectivism, Emmanuel Goldstein said that: