"Picardy" is a hymn tune used in Christian churches, based on a French carol; it is in a minor key and its meter is 8.7.8.7.8.7. Its name comes from the province of France from where it is thought to originate. The tune dates back at least to the 17th century, and was originally used for the folk song "Jésus-Christ s'habille en pauvre". First published in the 1848 collection Chansons populaires des provinces de France, "Picardy" was most famously arranged by Ralph Vaughan Williams in 1906 for the hymn "Let All Mortal Flesh Keep Silence", in The English Hymnal, the words of which are taken from the Byzantine Greek Liturgy of St. James translated by Gerard Moultrie a third master and chaplain at Shrewsbury School.
In addition, Gustav Holst used the hymn in his "3 Festival Choruses" Op. 36a.
While "Let All Mortal Flesh Keep Silence" is the most popular hymn for this tune, it is not the only one. "Christians, Let Us Love One Another" uses this same tune and has been sung in churches as well for many years.