Dumbledore's Army, or DA, is a secret Defence Against the Dark Arts group formed in 1995 and led by Harry Potter. After Lord Voldemort and his Death Eaters took over Hogwarts School of Witchcraft and Wizardry in 1997, Dumbledore's Army formed a resistance in Hogwarts School, culminating in the Battle of Hogwarts. The Headquarters was in the Room of Requirement within Hogwarts Castle.
 Book Five
The group was suggested to Harry by his friend, Hermione Granger, in response to the tyrannical rule of current Defence Against the Dark Arts teacher, Professor Dolores Umbridge. After initially being angry at the idea of teaching Defence Against the Dark Arts when he feels that he's unqualified since his reputation was built around things he only did by luck, he eventually relents.
Hermione invited twenty-five students in addition to herself, Harry, and Ron to meet in the Hog's Head pub in Hogsmeade to discuss forming the group. They agreed to form the group and all signed their names on a piece of parchment to agree not to tell anyone else what they were doing. However they were overheard by Willy Widdershins, who reported to the Ministry of Magic and to Umbridge , and by Mundungus Fletcher, who reported to the Order of the Phoenix. In response, the Ministry of Magic passed Educational Decree Number Twenty-four, banning all student organizations that do not have permission to reform from Umbridge.
Undeterred, they go ahead anyway, and begin looking for a suitable place to meet. Harry hears about the Room of Requirement, a room that only appears when someone has real need of it and is always equipped with the seeker's needs, from Dobby the house elf. This proved perfect for their purpose. In their first meeting there, they officially appointed Harry as leader and gave themselves a name; Cho Chang suggests the Defence Association, or the DA for short, and Ginny Weasley latches on to the idea and comes up with the name Dumbledore's Army, as that was the Ministry's real fear.
The DA were able to meet up frequently at an irregular pace thanks to Hermione creating magical fake Galleons with a Protean Charm on them, so that when Harry changed the numbers around the edge on his, the numbers would change on all the others. These numbers would represent the date and time of the next meeting.
The meetings were put to a stop by Umbridge after one DA member, Marietta Edgecombe, betrayed them to her. Marietta fell victim to a curse which Hermione had put on the parchment they had all signed at the start of the year, which caused pimples to spell out the word 'SNEAK' over her face, and as a result was unable to tell Umbridge everything. However, what she had said was enough for Umbridge to send her Inquisitorial Squad to catch them. Dobby heard about this in advance and warned them, but Draco Malfoy was able to catch Harry before he could escape, and they found the list of members in the Room of Requirement. Harry and Marietta were brought to Albus Dumbledore's office where the Minister for Magic, Cornelius Fudge, was waiting with two Aurors, John Dawlish and Kingsley Shacklebolt, the latter secretly a member of the Order of the Phoenix. In order to protect Harry, Dumbledore claimed responsibility for the group even though he'd had nothing to do with it, and a Memory Charm placed on Marietta by Kinglsley allowed her to corroborate his story. As a result, he had to leave the school.
Near the end of the school year, Harry had a vision of Order of the Phoenix member, Sirius Black, being tormented by Voldemort in the Department of Mysteries. DA members Ginny Weasley and Luna Lovegood help create a distraction so that Harry can see if this vision was true; however he, Ron, Hermione, Ginny, Luna, and Neville are all caught by Umbridge, who had become Headmistress of Hogwarts. Hermione and Harry successfully get rid of Umbridge in the Forbidden Forest, and the others managed to overpower the members of the Inquisitorial Squad holding them in her office. They then all convinced Harry to allow them to come with him to the Department of Mysteries.
Using Thestrals, they arrived at the suspiciously empty Ministry of Magic. In the Department of Mysteries they find a prophecy concerning Harry and an ambush of Death Eaters led by Lucius Malfoy waiting for him. They managed to fight them off for a while; however, Hermione was seriously injured, Ginny broke her ankle, Neville had his nose broken, Ron was hit by a curse that made him act oddly, and Luna was knocked out. Only Neville was there to help when the Death Eaters finally cornered Harry. He was quickly captured by Bellatrix Lestrange, but they were rescued by Dumbledore and the Order of the Phoenix's timely arrival. The prophecy was damaged in the skirmish and Sirius Black was killed; however, the DA members all survived. Harry was the only one of them left to face Voldemort in the Atrium.
 Book Six
Following the sacking of Dolores Umbridge and the appointment of Severus Snape as the new Defence Against the Dark Arts teacher, Dumbledore's Army stopped meeting. However, at the end of the school year, Harry hastily calls them using their coins to guard the castle when he is convinced that Draco Malfoy will succeed in whatever task it was that Voldemort had set him. This turned out to be to bring Death Eaters into the castle, and Malfoy did succeed. Only Luna Lovegood and Neville Longbottom answered the call, the former helping Hermione guard Snape and the latter fighting with the members of the Order of the Phoenix against the Death Eaters beneath the entrance to the Astronomy Tower.
 Final Book
- ↑ J. K. Rowling, OotP 15
- ↑ J. K. Rowling, OotP 16
- ↑ J. K. Rowling, OotP 27
- ↑ J. K. Rowling, OotP 17
- ↑ J. K. Rowling, OotP 18
- ↑ J. K. Rowling, OotP 19
- ↑ J. K. Rowling, OotP 27
- ↑ J. K. Rowling, OotP 31
- ↑ J. K. Rowling, OotP 32
- ↑ J. K. Rowling, OotP 33
- ↑ J. K. Rowling, OotP 34
- ↑ J. K. Rowling, OotP 35
- ↑ J. K. Rowling, OotP 36