Slipjoint folders were some of the first folding knives ever. While they are not the only traditional folding mechanism, they are the one that has remained the most popular in the modern age. Slipjoint use a backspring (just like a lock back), but not notch to lock the blade open. The spring has a flat side that mates with the flat tang on the knife. They lock together sort of like a clutch. When enough pressure is applied to the spine of the blade, it pushes the backspring out of the way and allows the blade to close. While there is no actual lock or release mechanism, the slipjoint is not a friction folder (which stays open purely from the friction at the pivot).

Slipjoints are very collectable. Many brands such as Case, Queen, and Hen and Rooster create slipjoints specifically as collectables. Most production slipjoints are inexpensive, but custom and handmade slipjoints can be some of the most expensive knives on the market. Bill Ruple is a notable maker of state of the art (though still traditional) handmade slipjoints.

Slipjoints come in many different patterns, usually named after the intended use. Som e slipjoints have one blade, some have two or more. Different blade configurations make the knife more or less suited to different kinds of work. A farmer would need different blades than a leather worker.

Slipjoints are great pocket knives because they are easy to carry, are not threatening, and tend to be very versatile. However, slipjoints cannot do what modern locking folders, or fixed blades, can do. Slipjoints are for light utility work, not heavy use.