The Diet of Worms (in German: Wormser Reichstag) was, like any Reichstag in the Holy Roman Empire, an official governmental and religious council session. Headed by Emperor Charles V, it took place in Worms, Germany, a small town on the Rhine river, from January 28 to May 25, 1521.

Although other issues were addressed at the Diet of Worms, it is most remembered for its handling of Martin Luther and the subsequent effects on the Protestant Reformation. Luther was called upon to recant his teachings, yet he defended them and called for reform from April 16 - April 18, 1521. He was ordered to leave Worms on April 25 or 26. On May 25, the Edict of Worms declared Luther to be an outlaw.

In Shakespeare's Hamlet, he says: "..your worm is your only emperor for diet" (IV.iii)

This can mean either diet in the traditional sense or diet in the political sense.