Almost a partner word to folding, locking is the second designation of a folding knife, should it have a system whereby the blade is locked in place until a release switch or lever is depressed. The most common lock is a 'liner-lock' where the inner metal frame is bent up to form a mechanical spring button, with a flat edge that will click into place against the rear side of the blade when it is extended. pressure on a tab or button attatched (or built into) this spring releases the lock and allows the blade to be retracted. This method requires the operator's fingers or thumbs to be in the blade's path and care should always be taken when operating such a locking mechanism. Currently SOG hold the patent on their 'piston-lock' system where the blade is held in the extended position by a piston and the release lever is mounted through the knife's handle scales. This enused that the blade can be retracted safely without ever putting one's fingers in the path of the blade.

Although the durability and usage tolerances of a locking blade are superior to those of a non-locking blade, for heavy duty or regular use, a knife with a solid tang is preferable.