thumb|right|270px|Ancient Roman earthenware flagons
A flagon () is a large leather, metal, glass, plastic or ceramic vessel, used for storing and pouring drink, whether this be water, ale, or another liquid. They are generally not intended to be drunk from directly, like a cup or tankard. A flagon is typically of about in volume, and it has either a handle (when strictly it is a jug), or (more usually) one or two rings at the neck. Sometimes the neck has a large flange at the top rather than rings. The neck itself may or may not be formed into one, two or three spouts. The name comes from the same origin as the word "flask".
Christian use
thumb|[[Hardman & Co. communion flagon from the mid-19th century]]
As a Roman Catholic term of use, the flagon is the large vessel, usually glass and metal, that holds the wine. Before March 2002, a flagon may have also been used to hold the wine during the consecration of the Eucharist and then be poured into many chalices. This pouring of sacramental wine from flagon to chalice was eliminated. A smaller container called a cruet is used for the priest's chalice, usually identical to the cruet of water, which is mingled with the wine before consecration. The cruets do not remain on the altar after the preparation of the gifts.
In the Evangelical-Lutheran Churches, the flagon typically has the design of the pelican engraved on it, or "the vine and its fruit". The flagon is made of gold.