In the Roman calendar, the Ides of March was a term used to denote 15 March. In general, the Ides fell on the 15th day of the months of March, May, July, or October, or the 13th day of any other month.

The term had real meaning only in the traditional Roman calendar, which was displaced by the Julian calendar in 46 BC; however, it was still used in a colloquial sense for centuries afterwards to denote the middle of the month.

In modern times, the term is best known because of Julius Caesar having been assassinated on the Ides of March in 44 BC, the story of which was famously retold in William Shakespeare's play Julius Caesar.

The term has come to be used as a metaphor for impending doom.