Dumbledore's Army (The D.A.) is a fictional organisation founded in Harry Potter and the Order of the Phoenix, the fifth book in the Harry Potter series by J.K. Rowling.

In the book, Hogwarts High Inquisitor Dolores Umbridge decided to teach only the theory in her Defence Against the Dark Arts classes for political reasons. This move was widely unpopular among the student body, causing Hermione Granger to suggest the founding of their own group where Harry Potter (who had accumulated quite a lot of experience on the subject) would teach all those interested in practical Defence Against the Dark Arts.

Hermione found "a few people" (who turned out to be over twenty) to meet Harry, Ron, and Hermione in the Hog's Head to discuss the founding of the group. This went directly against the aims of Umbridge, who learned of the meeting and banned all student organizations not approved by her. The newly-formed group responded by going underground and afterwards took residence in the Room of Requirement, where it met about once a week for several months. It took the name Dumbledore's Army to ridicule Umbridge's previously mentioned political reasons. Later on, when Dumbledore finds out what the name of the group is, it is implied that he is deeply touched by their show of loyalty.

In the end, Cho Chang's friend Marietta Edgecombe betrayed the group to Umbridge. To avoid Harry getting thrown out of the school, Albus Dumbledore managed to frame himself for organizing the group. Being the wizard that he is, he then escaped from Hogwarts without much difficulty.

Though the D.A. stopped meeting after this, what the students learned came in handy. Six members of the D.A. (Harry Potter, Ron Weasley, Hermione Granger, Neville Longbottom, Ginny Weasley and Luna Lovegood) were involved in the battle against Death Eaters in the Department of Mysteries. Only Harry and Neville were left standing by the end, and Neville may have been driven insane had members of the Order of the Phoenix not arrived, while Harry was spared because he held the prophecy that Voldemort did not want damaged. None of the D.A. members suffered permanent damage in the battle, though Order member Sirius Black was killed in action.

Members of Dumbledore's Army

• Hannah Abbott
• Lavender Brown
• Katie Bell
• Susan Bones
• Terry Boot
• Cho Chang
• Michael Corner
• Colin Creevey
• Dennis Creevey
• Marietta Edgecombe (formerly)
• Justin Finch-Fletchley
• Seamus Finnigan
• Anthony Goldstein
• Hermione Granger (deputy)
• Angelina Johnson
• Lee Jordan
• Neville Longbottom
• Luna Lovegood
• Ernie Macmillian
• Padma Patil
• Parvati Patil
• Harry Potter (leader and D.A. teacher)
• Zacharias Smith
• Alicia Spinnet
• Dean Thomas
• Fred Weasley
• George Weasley
• Ginny Weasley
• Ron Weasley