For the starship class used by Starfleet in the 22nd century, see NX class.

NX has been a prefix for Federation starship registry numbers since its inception in the late 22nd century, derived from the NCC prefix of the Federation Starfleet.

"NX" stands for "Naval, eXpermimental", and can refer to any vessel that contains entirely new technologies and/or design concepts--such as the four-nacelle USS Constellation (NX-1974)--or merely the first starship of a particular class--such as the new-design USS Excelsior (NX-2000)--before it is approved for class production.

It is not necessarily applied to all ships that are the first member of their class, especially if it is known that the class is being immediately put into serial production.