The Affair of the Diamond Necklace is a mysterious incident in the 1780s at the court of Louis XVI of France involving his wife, Queen Marie Antoinette.

The reputation of the Queen, which is already tarnished by gossip, is ruined by the implication that she has participated in a crime to defraud the crown jewelers of the cost of a very expensive diamond necklace.

The Affair is historically significant as one of the events that leads to the French populace's disillusionment with the monarchy, which, among other causes, eventually culminates in the French Revolution.