They are not made by the U.S. Mint — instead, they are made by private minting firms.
And they are not used as currency.
Challenge coins are small medallions or novelty pieces that carry the name or logo of an organization and also bear an emblem or insignia representing that organization.
They were traditionally issued to members of organizations when challenged to prove membership (sort of like an ID card), and they are often carried by members of the military.
Challenge coins first made their appearance during World War I. They are still issued by many organizations and fraternities today.
They are widely popular collectibles.
