A keychain or key chain is a small chain, usually made from metal or plastic, that connects a small item to a keyring. The length of a keychain allows an item to be used more easily than if connected directly to a keyring. Some keychains allow one or both ends the ability to rotate, keeping the keychain from becoming twisted, while the item is being used. A keychain can also be a connecting link between a keyring (a.k.a. "split ring") and the belt of an individual.

A keychain can also be a short chain used to link together a number of keys or other items. Sometimes keychains are even hung on walls.

In the 1950s and 1960s with the improvement of plastic manufacturing techniques, promotional items including keychains became more unique. Businesses could place their names on promotional keychains that were three dimensional for less expensive than the standard metal keychains.

Keychains that currently hold keys are an item that is never long misplaced by the owner. Many keychains also offer functions that the owner wants easily accessible as well. These include an army knife, bottle opener, an electronic organizer, scissors, address book, family photos, nail clipper, pill case and even pepper spray. Modern cars often include a keychain that serves as a remote to lock/unlock the car or even start the engine. An electronic key finder is also a useful item found on many keys that will beep when summoned for quick finding when misplaced.

Keychains are one of the most common souvenir items. They are very inexpensive and small to store both while traveling home and don't take up much room in a home. Keychains can act as a reminder of the trip since they can be carried around during everyday life. They also are gender and age neutral and can appeal to many types of vacation shoppers.

The costs of keychains vary widely depending on their purpose. Advertising keychains begin at only a few cents a piece to a few dollars each. They are normally purchased in large quantities often over 500 at a time.

Souvenir keychains are one of the most popular keychains that sell. These are keychains that represent a trip or a location that a person is visiting. These most commonly range from under a dollar to 10 dollars.

Unlike most collections, keychains don't hold their value as well as other collections. A standard keychain that was purchased for five dollars new is often only worth a quarter once it has been owned regardless of condition.