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. It is usually employed by personnel whose job demands frequent use of keys, such as a security guard, prison officer, janitor, or retail store manager. The chain is often retractable, and therefore may be a nylon rope, instead of an actual metal chain. The chain ensures that the keys remain attached to the individual using them, makes accidental loss less likely, and saves on wear and tear on the pockets of the user.

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.

Keychains are commonly used to promote businesses. A standard advertising key chain will carry the businesses name and contact information and often a logo. The most popular advertising keychains are shaped like a "number 1" to imply the quality of the business that is advertising. Other popular shapes are a house, owl and squares or rectangles.

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 are small and inexpensive enough to become promotional items for larger national companies that might give them out by the millions. For example, with the launch of a new movie or television show, those companies might partner with food companies to provide a character keychain in each box of cereal etc.

 
A souvenir sandal keychain from the PhilippinesKeychains 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.