Klagt, Kinder, klagt es aller Welt, also known as Köthener Trauermusik, BWV 1143, BWV 244a, is a cantata by Johann Sebastian Bach. He composed it in 1729 for the funeral of Leopold, Prince of Anhalt-Köthen. The music is lost, but the libretto survives. As Bach is known to have used musical material which also appeared in two surviving works, one being the St Matthew Passion, it has been possible to make reconstructions.

The cantatas composed by Johann Sebastian Bach, known as Bach cantatas, are a body of work consisting of over 200 surviving independent works, and at least several dozen that are considered lost. As far as known, Bach's earliest cantatas date from 1707, the year he moved to Mühlhausen, although he may have begun composing them at his previous post in Arnstadt. Most of Bach's church cantatas date from his first years as Thomaskantor and director of church music in Leipzig, a position which he took up in 1723.