A challenge coin is a small coin or medallion, bearing an organization's insignia or emblem and carried by the organization's members. Traditionally, they might be given to prove membership when challenged and to enhance morale. They are also collected by service members and law enforcement personnel. Historically, challenge coins were presented by unit commanders in recognition of special achievement by a member of the unit. They could also be exchanged in recognition of visits to an organization.[1]

‍Modern day challenge coins may feature popular culture attributes[2] or organizational values.[3] Modern challenge coins are made in a variety of sizes and are often made using popular culture references, including superheroes and other well known characters in a way that creates a parody.

Challenging
The tradition of a challenge is the most common way to ensure that members are carrying their unit's coin. The rules of a challenge are not always formalized for a unit, and may vary between organizations. The challenge only applies to those members that have been given a coin formally by their unit. This may lead to some controversy when challenges are initiated between members of different organizations and is not recommended. The tradition of the coin challenge is meant to be a source of morale in a unit, and forcing the challenge can cause a reverse effect. The act of challenging is called a "coin check" and is usually loudly announced.[15][19][28]

‍The challenge, which can be made at any time, begins with the challenger drawing his/her coin, and slapping or placing the coin on the table or bar. In noisy environments, continuously rapping the challenge coin on a surface may initiate the challenge. (Accidentally dropping a challenge coin is considered to be a deliberate challenge to all present.) Everyone being challenged must immediately produce the coin for their organization and anyone failing to do so must buy a round of drinks for the challenger and everyone else who has their challenge coin. However, should everyone challenged be able to produce their coin, the challenger must buy a round of drinks for the group.[15][18][19]

‍While most holders of challenge coins usually carry them in their pockets or in some other readily accessible place on their persons, most versions of the rules permit a challenged person "a step and a reach" or if an individual has an extra coin to pass it off to the person closest to them. Coins on belt buckles or key chains are not acceptable for meeting a challenge. However, a coin worn around the neck is acceptable for meeting a coin challenge.[18][19][28]

‍Variants of the rules include, but are not limited to, the following: If someone is able to steal a challenge coin, everyone in the group must buy a drink for that person. During a challenge, everyone in the group must buy a drink for the holder of the highest-ranking coin.

A coin's rank is determined by the rank of the giver of the challenge coin. For example, a coin presented by an Admiral would outrank a coin presented by a Vice Admiral, while both would outrank a coin presented by a Captain. Traditionally, the presentation of a coin is passed during a handshake. Some units provide strict time limits to respond to a challenge. Also coins are ranked in level of difficulty in attaining them. An Infantryman coin would outrank a logistical coin. A Ranger coin would outrank an Infantryman coin.

Traditionally, rules of a challenge include a prohibition against defacing the coin, especially if it makes it easier to carry at all times. If the challenge coin is attached to a belt buckle or key ring, or has had a hole drilled in it to attach to a lanyard, it no longer qualifies as a challenge coin.[19][29]