"Mack the Knife" or "The Ballad of Mack the Knife", originally "Die Moritat von Mackie Messer", is a song composed by Kurt Weill with lyrics by Bertolt Brecht for their music drama Die Dreigroschenoper, or, as it is known in English, The Threepenny Opera. It premiered in Berlin in 1928.

A moritat (from mori meaning "deadly" and tat meaning "deed") is a medieval version of the murder ballad performed by strolling minstrels

The Brecht-Weill version of the character was far more cruel and sinister, and has been transformed into a modern anti-hero.

The opera opens with the moritat singer comparing Macheath (unfavorably) with a shark, and then telling tales of his robberies, murders, rapes, and arson.