Prime Directive

Save the hippies!

The Prime Directive is the Federation Starfleet's most important regulation. It forbids interference with alien cultures more primitive than the Federation. In TOS, it was more of a loose guideline that was subject to the Captain's discretion, and Kirk was known to throw it out the window on more than one occasion. In TNG, the interpretation is much more strict, and many times it led to a decision to allow an entire species go extinct.