Unser Mund sei voll Lachens, BWV 110

Unser Mund sei voll Lachens ('May our mouth be full of laughter'), BWV 110, is a church cantata by Johann Sebastian Bach. He composed the Christmas cantata in Leipzig for Christmas Day and first performed it on 25 December 1725.

When Bach wrote the music, he was in his third year as Thomaskantor, the church music director of Leipzig. After months with only a few cantata compositions, he embarked on a set of five cantatas for Christmas occasions. In four of these, he used earlier texts published in 1711 by Georg Christian Lehms. The text for this cantata has no pairs of recitative and arias as is common in Baroque opera and contemporary Bach cantatas. Using an older style, it instead features three biblical quotations – verses from Psalm 126, a verse from the Book of Jeremiah about God's greatness, and the angels' song from the Nativity according to the Gospel of Luke – alternating with arias. The closing chorale is from Kaspar Füger's hymn "Wir Christenleut".

Bach composed the work in seven movements and scored it festively for four vocal soloists, a four-part choir and a Baroque instrumental ensemble with trumpets and timpani, flutes and several kinds of oboe. The outer movements are given to the choir and the full orchestra; the inner movements are chamber music for solo voices and solo instruments. Bach derived the first chorus, which is in the style of a French overture, from the first movement of his fourth Orchestral Suite. He embedded vocal parts in its fast middle section, illustrating the laughter mentioned in the psalm verse. The song of the angels is based on the Christmas interpolation Virga Jesse Floruit from his Magnificat in E-flat major, BWV 243a. He chose obbligato instruments to differentiate the character of the three arias: two flutes with the tenor expressing the "lowly birth", oboe d'amore with the alto, representing God's love, and trumpet, oboes and strings with the bass for his call to sing songs of joy together. Bach led the Thomanerchor in the first performances on Christmas Day in two Leipzig churches.