A shadowy organisation operating outside Starfleet's chain of command in defence of the Federation.
Section 31 is a secret intelligence organisation that claims to protect the Federation by any means necessary, including deception, sabotage and murder. It takes its name from Article 14, Section 31 of the Starfleet Charter, which allows extraordinary measures in times of extreme threat. It is not an actual place, but an organisation that answers to no one.
Section 31 first appeared in the Deep Space Nine episode Inquisition, in which the agent Luther Sloan tries to recruit Julian Bashir. Later the crew learned that the Section had deliberately infected the Founders with a deadly disease. In Extreme Measures, Bashir and O'Brien enter the dying Sloan's mind to find the cure, which Odo then passes to the Founders.
The organisation also appears in Enterprise, where it pressures Malcolm Reed into working for it, in Star Trek Into Darkness, and in Discovery, where it is run by Leland and later threatened by its own AI, Control. Philippa Georgiou of the mirror universe joins it, and she leads a Section 31 team in the 2025 film Star Trek: Section 31.