Room 101 is a place introduced in the novel Nineteen Eighty-Four by George Orwell. It is a torture chamber in the Ministry of Love in which the Party attempts to subject a prisoner to his or her own worst nightmare, fear or phobia.
You asked me once, what was in Room 101. I told you that you knew the answer already. Everyone knows it. The thing that is in Room 101 is the worst thing in the world.
Such is the purported omniscience of the state in the society of Nineteen Eighty-Four that even a citizen's nightmares are known to the Party. The nightmare, and therefore the threatened punishment, of the protagonist Winston Smith is to be attacked by rats. Smith saves himself by begging the authorities to let his lover, Julia, have her face gnawed by the ferocious rodents instead. The torture, and what Winston does to escape it, breaks his last promise to himself and to Julia: never to betray her emotionally. The book suggests that Julia is likewise subjected to her own worst fear, and when she and Winston later meet in a park, he notices a scar on her forehead. The original intent of threatening Winston with the rats was not necessarily to go through with the act, but to force him into betraying the only person he loved and therefore break his spirit.

Orwell named Room 101 after a conference room at BBC Broadcasting House where he used to sit through tedious meetings.

The novel's popularity has resulted in the term "Room 101" being referred to in many fictional works. For example, in the tabletop role-playing game Mage: The Ascension, many members of the Technocratic Union are mages who have been kidnapped and "processed" (indoctrinated) in the infamous "Room 101", and "deviants" are otherwise sent there for a torturous re-conditioning process.

Room 101 has also become a popular name for a place where unpleasant things are done. On the British TV show Room 101, celebrities are interviewed and asked to list their pet peeves, which are then condemned to the unseen room, or not, at the discretion of the host.

In the 2005 series of Big Brother (UK), a housemate was required to enter a Room 101 to complete tedious and unpleasant tasks, including sorting different colours of maggots.

There is a song by Carcass named Room 101 on their album Swansong.

In The League of Extraordinary Gentlemen: Black Dossier, the physical location of Room 101 (and the Ministry of Love) is given as the MI6 headquarters at Vauxhall Cross.

According to Anna Funder's book Stasiland, Erich Mielke, the last Minister of State Security (Stasi) of the former GDR, had the floors of the Stasi headquarters renumbered so that his second floor office would be number 101.

When one of the possible original room 101s at the BBC was due to be demolished, a plaster cast was made by artist Rachel Whiteread. The cast was displayed in the cast courts of the Victoria and Albert Museum from November 2003 until June 2004