A pyx or pix is a small round container used in the Catholic, Old Catholic, Lutheran and Anglican Churches to carry the Eucharist, to the sick or those who are otherwise unable to come to a church in order to receive Holy Communion. The term can also be used in archaeology and art history to describe small, round lidded boxes designed for any purpose from antiquity or the Middle Ages, such as those used to hold coins for the Trial of the Pyx in England.

The Trial of the Pyx is a judicial ceremony in the United Kingdom to ensure that newly minted coins from the Royal Mint conform to their required dimensional and fineness specifications. Although coin quality is now tested throughout the year under laboratory conditions, the event has become an annual historic tradition. Each year, thousands of coins are put on trial, consisting of both those struck for circulation and non-circulating commemorative coins.