SPECTRE ("Special Executive for Counter-intelligence, Terrorism, Revenge and Extortion") is a fictional organisation featured in the James Bond novels by Ian Fleming, as well as films and video games based in the same universe. Led by criminal mastermind Ernst Stavro Blofeld, SPECTRE first formally appeared in the novel Thunderball (1961) and in the film Dr. No (1962). The international organisation is not aligned with any nation or political ideology, enabling the later Bond books and Bond films to be regarded as somewhat apolitical. The presence of former Gestapo members in the organization can be considered as a sign of Fleming's warnings about Nazi fugitives after the Second World War, as first detailed in the novel Moonraker (1955). In the novels, SPECTRE begins as a small group of criminals, but in the films it is depicted as a vast international organisation with its own SPECTRE Island training base capable of replacing the Soviet SMERSH.

In the James Bond novels, SPECTRE is an organised crime enterprise led by Ernst Stavro Blofeld. The organisation's executive consists of 21 individuals, 18 of whom handle day-to-day affairs. Members are drawn in groups of three from six of the world's most notorious organisations — the Nazi German Gestapo, the Soviet SMERSH, Yugoslav Marshal Josip Broz Tito's OZNA, the Italian Mafia, the French-Corsican Unione Corse, and KRYSTAL, a massive Turkish heroin-smuggling operation. Coincidentally, the three from KRYSTAL are all former members of RAHIR, an intelligence agency previously run by Blofeld. The remaining three members are Blofeld himself and two scientific/technical experts who make their debut in the ninth Bond novel, Thunderball (1961). When Ian Fleming was writing the novel in 1959, he believed that the Cold War might end during the two years it would take to produce the film, and he came to the conclusion that the inclusion of a contemporary political villain would leave the film looking dated. Therefore, he thought it better to create a politically neutral enemy for Bond. Fleming's SPECTRE has elements inspired by mafia syndicates and organised crime rings that were actively hunted by law enforcement in the 1950s. The strict codes of loyalty and silence, and the hard retributions that followed violations, were hallmarks of American gangster rings, the Italian Mafia, the Russian mafia, the Unione Corse, the Chinese Tongs and Triads, and the Japanese Yakuza and Black Dragon Society. During the events of Thunderball, SPECTRE successfully hijacked two nuclear warheads for ransom.

The organisation is next mentioned in the tenth novel, The Spy Who Loved Me (1962), when James Bond describes investigating their activities in Toronto before the story begins, though they play no part in the story itself. The organisation's third appearance is in the eleventh novel, On Her Majesty's Secret Service (1963) where Blofeld, hired by an unnamed country or party—though the Soviet Union is implied—is executing a plan to ruin British agriculture with biological warfare. Blofeld, with a weakened SPECTRE, would appear for the final time in the twelfth novel, You Only Live Twice (1964). By this point, the organisation has largely been shut down, and what remains is focused on maintaining Blofeld's alias as Dr. Guntram von Shatterhand and his compound in Japan.

In the films, the organisation often acts as a third party in the ongoing Cold War. Their objectives have ranged from supporting Dr. Julius No (Joseph Wiseman) in sabotaging American rocket launches, holding the world to ransom, and demanding clemency from governments for their previous crimes. The goal of world domination was only ever stated in the film version of You Only Live Twice (1967) when SPECTRE was working on behalf of an unnamed Asian government. This is strongly implied to be Red China, who earlier backed Auric Goldfinger (Gert Fröbe) in the 1964 film of the same name.

Its long-term strategy, however, is illustrated by the analogy of the three Siamese fighting fish Blofeld keeps in an aquarium aboard SPECTRE's yacht in the film version of From Russia with Love (1963). Blofeld notes that one fish is refraining from fighting two others until their fight is concluded. Then, that cunning fish attacks the weakened victor and kills it easily. Thus SPECTRE's main strategy is to instigate conflict between two powerful enemies, namely the superpowers, hoping that they will exhaust themselves and be vulnerable when it seizes power. SPECTRE thus works with, and against, both sides of the Cold War. For example, in the film Thunderball (1965), it simultaneously blackmails a Japanese double agent, distributes Red Chinese narcotics in the United States, kills a defector to the USSR on behalf of the French Foreign Ministry, and threatens NATO with stolen nuclear weapons, while continuing ordinary criminal operations such as advising on the British Great Train Robbery.

In both the film and the novel Thunderball, the physical headquarters of the organisation are in Paris, operating behind a front organisation aiding refugees named "Firco" (Fraternité Internationale de la Résistance Contre l'Oppression) in the novels and "International Brotherhood for the Assistance of Stateless Persons" in the films. Organisational discipline is notoriously draconian, with the penalty for disobedience or failure being death. To heighten the impact of executions, Blofeld had been known to focus attention on an innocent member, making it appear his death is imminent, only to suddenly strike down the actual target when that person is off guard.

SPECTRE is headed by the criminal mastermind Ernst Stavro Blofeld who usually appears accompanied by a Chinchilla Silver Persian cat in the films, but not in the books. In both the films and the novels, Emilio Largo (played in the film Thunderball by Adolfo Celi) is the second in command. It is stated in the novel that if something were to happen to Blofeld, Largo would assume command. Largo appears in the 1961 novel Thunderball, the 1965 film version and its 1983 remake, Never Say Never Again, where he is renamed Maximilian Largo (Klaus Maria Brandauer) and is said to be Romanian rather than Italian.

The SPECTRE cabinet had a total of twenty-one members. Blofeld was the chairman and leader because he founded the organisation and Largo was elected by the cabinet to be second in command. A physicist named Kotze (who later defected) and an electronics expert named Maslov were also included in the group for their expertise on scientific and technical matters.