Fantasia sur « Wo Gott der Herr nicht bei uns halt », BWV 1128

Wo Gott der Herr nicht bei uns hält is a chorale fantasia for organ composed by Johann Sebastian Bach, likely between 1705 and 1710. The Zahn 4441a hymn tune for Justus Jonas's 1524 hymn "Wo Gott der Herr nicht bei uns hält", a paraphrase of Psalm 124, is the basis of the composition.

A copy of the work resurfaced on 15 March 2008 at an auction of items from the collection of the 19th-century Bach scholar Wilhelm Rust. The piece, until then known as BWV Anh. 71, was thus authenticated as Bach's and was reassigned the number BWV 1128.