Starfleet General Order 1, the Prime Directive forbids its officers from interfering in the natural development of other civilisations, above all those that have not yet discovered warp travel.
The Prime Directive is Starfleet's General Order 1 and the best-known rule in the service. It forbids interference in the internal affairs and natural development of other cultures, and in particular bars officers from revealing advanced technology or the existence of other worlds to societies that have not yet achieved warp flight. Captains are expected to give up their ships and their lives rather than break it.
It is first named in The Return of the Archons and is tested in A Private Little War, Bread and Circuses, The Omega Glory and Patterns of Force. Later crews wrestle with it in Pen Pals, Who Watches the Watchers, Symbiosis and Homeward, while Dear Doctor shows Archer reasoning his way towards it before it existed.
The pilot of Strange New Worlds ends with General Order 1 being given its more famous name after Pike breaks it on Kiley 279.