The only relic once belonging to Rowena herself, granted the wearer enhanced wisdom and knowledge. It is assumed that Rowena is the creator of the enchantment, but it has never been confirmed, nor denied. Rowena had her famous quote "Wit beyond measure is man's greatest treasure." etched into the side of the head piece. The Diadem was silver in color, with a large blue sapphire in the center.

As discussed in an earlier chapter, the Diadem is eventually turned into one of Lord Voldemort's Horcrux's. This event makes the ghost of Helena Ravenclaw increasingly depressed and guilty. It is revealed in the last book/movie that Helena was the one who gave the Diadem to Tom Riddle, who convinced Helena he would destroy it for her.

The famous Harry Potter discovered the Diadem once in the "room for hidden things", within the Room of Requirement, not knowing what it was, he places the Diadem on a bust of an old warlock. Later the next year Harry returns with new information from Helena, and the intent to destroy the Diadem. Harry is confronted by Draco Malfoy, Gregory Goyle, and Vincent Crabbe. In the 'heat' of battle, Crabbe conjures Fiendfyre, which spirals out of his control. The spell then starts the entire room on fire, resulting in his own death, as well as the destruction of the Diadem.