Handcuffs are restraints designed to hold a person's wrists together. They consist of two parts, connected by chains, hinges or rigid bars. Each half has a rotating arm that engages with a ratchet to prevent the ratchet from opening once it is closed on a person's wrist. Without a key, the handcuffs cannot be removed, so the handcuffer's wrists cannot be separated by more than a few centimeters per inch, making many tasks difficult or impossible. This is usually done to prevent suspected criminals from escaping police custody.

There are three main types of modern metal handcuffs: chain (handcuffs are held together by short chains), hinge (because hinge handcuffs allow less movement than chain handcuffs, they are generally considered safer) and solid handcuffs. Although it's bulky to carry, hard handcuffs allow a variety of changes to the cuff. Hiatts speedcuffs are hard handcuffs used by most British police. Both rigid and hinged cuffs can be used with one hand for pain relief / control techniques that are not suitable for chain cuffs. Various accessories can be used to improve safety or rigidity of handcuffs, including boxes that can be mounted on chains or hinges and can be locked by padlocks themselves.