The Marauder's Map reveals the locations of everyone inside Hogwarts in J.K. Rowling's Harry Potter series.
Harry receives the map from Fred and George Weasley in Harry Potter and the Prisoner of Azkaban. When activated with the phrase “I solemnly swear that I am up to no good,” it displays the castle's rooms, passages, grounds, and moving labels for people within its range.
The map was created by four Hogwarts students who called themselves the Marauders: James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew. Their school nicknames were Prongs, Padfoot, Moony, and Wormtail.
The map is especially important because it exposes hidden routes and can identify people who are nearby. It is not the same as the Mirror of Erised, which shows a viewer's deepest desire, or a Pensieve, which stores and displays memories. Its apparent ability to recognize its creators also becomes important later.