Occlumency

Occlumens and Legilimens Severus Snape attempting to train Harry Potter in Occlumency.

Severus Snape: "The headmaster has sent me to tell you, Potter, that it is his wish for you to study Occlumency this term."

Harry Potter: "Study what?"

Severus Snape: "Occlumency, Potter. The magical defense of the mind against external penetration. An obscure branch of magic, but a highly useful one."

— Severus Snape, an accomplished Occlumens, telling Harry Potter about Occlumency in 12 Grimmauld Place

Occlumency is the act of magically closing one's mind against Legilimency. It is ancient, and has existed since medieval times. It can prevent a Legilimens from accessing one's thoughts and feelings, or influencing them. A person who practises this art is known as an Occlumens.

Methods

"I told you to empty yourself of emotion! ... Fools who wear their hearts proudly on their sleeves, who cannot control their emotions, who wallow in sad memories and allow themselves to be provoked this easily — weak people, in other words — they stand no chance against his powers! He will penetrate your mind with absurd ease, Potter!"

— Severus Snape on the difficulty of learning Occlumency

The most basic form of Occlumency, judging from Severus Snape's early lessons on the subject to Harry Potter, involves clearing one's mind — making it "blank and empty" — in order to prevent a Legilimens from perceiving one's emotions and thoughts. More advanced Occlumency involves suppressing only the thoughts, emotions, and memories that would contradict whatever it is an Occlumens wishes a Legilimens to believe; hence, it is not obvious that Occlumency is being used even if the person is lying. It requires a great deal of will power, as with resisting the Imperius Curse, as well as a high degree of mental and emotional discipline. It is also one method of resisting the influence of Veritaserum.

Occlumency is not part of the normal curriculum taught at Hogwarts School of Witchcraft and Wizardry and appears to be a rare and difficult skill.

Examples

"Used properly, the power of Occlumency will help shield you from access or influence. In these lessons I will attempt to penetrate your mind. You will attempt to resist. Prepare yourself! Legilimens! "

— Snape during Harry Potter's Occlumency lesson

In the 1995–1996 school year, Albus Dumbledore had Severus Snape teach Harry Potter Occlumency in an effort to prevent his mind from being penetrated and influenced by Lord Voldemort. Snape was a highly skilled Occlumens, being able to successfully deceive extremely accomplished Legilimens Voldemort, but his lessons with Harry were ultimately unsuccessful. Harry was not able to repel most attacks, though it is likely that the personal enmity between him and Snape as well as the stressful events in his life that year hindered his ability. He eventually gave up attempting to learn. Harry later managed to block his connection to Voldemort, on occasion, by focusing on feelings of love and grief, rather than by using Occlumency.

Snape himself also employed Occlumency to hide his loyalty to the Order of the Phoenix from Voldemort, and due to his well-known mastery, both sides had difficulty trusting him.

In 1996, Bellatrix Lestrange trained her nephew, Draco Malfoy in Occlumency so that he could keep his mission to kill Albus Dumbledore a secret. Draco became skilled enough to repel Snape's attempts at Legilimency. Draco's success was due to him shutting out his compassion to become the bully he is, making it easy for him to close his mind.

Known Occlumens

Draco Malfoy, an occlumens

• Maxwell Barnett
• Barty Crouch Jr.
• Albus Dumbledore
• Bellatrix Lestrange
• Draco Malfoy
• Severus Snape
• Horace Slughorn
• Lord Voldemort
• Gellert Grindelwald (possibly)
• Narcissa Malfoy (possibly)
• Sirius Black (possibly)

Etymology

The word "occlumency" comes from the Latin occludere, meaning "to shut up" and mens, for "mind".

Behind the scenes

• On the subject of Occlumency, J. K. Rowling has discussed why Draco Malfoy would be skilled at it while Harry Potter was not:
  • "...I think Draco would be very gifted in Occlumency, unlike Harry. Harry’s problem with it was always that his emotions were too near the surface and that he is in some ways too damaged. But he's also very in touch with his feelings about what's happened to him. He's not repressed, he's quite honest about facing them, and he couldn't suppress them, he couldn't suppress these memories. But I thought of Draco as someone who is very capable of compartmentalising his life and his emotions, and always has done. So he's shut down his pity, enabling him to bully effectively. He's shut down compassion — how else would you become a Death Eater? So he suppresses virtually all of the good side of himself."
• Occlumency, being a "magical defense of the mind against external penetration" most likely will make the use of the curse against an Occlumens either ineffective or in the very least reduce its effectiveness, although this is unconfirmed.
• Occlumency does not appear to be generally offered subject of study at Hogwarts and is probably only taught in private courses to students who show potential for it.
• Narcissa Malfoy may be an Occlumens, as she lied to Voldemort about Harry's demise without consequences. However, Voldemort may not have been using Legilimency on her at the time, as he might not have believed she would lie to him with her family's lives at stake, a sign of Voldemort's greatest weakness: arrogance.
• Gellert Grindelwald may also have been an Occlumens, as he lied to Voldemort about having owned the Elder Wand. However, this is unconfirmed.
• According to W.O.M.B.A.T., it is possible that Occlumency can guard against possession.
• Voldemort employed Occlumency against Harry Potter to try to end the connection, but started to lose control during the events of 1997 and 1998.
• Harry Potter briefly used Occlumency against Voldemort, although he has never been able to master it. 
• Bellatrix Lestrange was most likely taught Occlumency by Voldemort, since she stated in the Battle of the Department of Mysteries that he taught her the dark arts. 
• Draco was most likely taught Occlumency by Bellatrix Lestrange, a theory made by Severus Snape when he tries, unsuccessfully, to break into Draco's thoughts. 
• Remus Lupin was able to conceal the fact that Sirius Black was an unregistered Animagus from Albus Dumbledore and Severus Snape, both highly skilled legilimens, throughout his entire tenure teaching at Hogwarts in spite of the latter's intense dislike for him and stated suspicion that he was aiding Sirius Black. Dumbledore only found out because Lupin told him voluntarily, and because Black revealed himself in front of Ron Weasley. It is unknown if he was using occlumency to conceal this knowledge or if Snape and Dumbledore just never used legilimency against him.
• The Wizengamot believed that Sirius Black might have been an Occlumens, as they believed that even if they give him a fair trial under the influence of Veritaserum, he would still be able to resist it with Occlumency or other tricks.

Appearances

• Harry Potter and the Order of the Phoenix (First appearance)
• Harry Potter and the Order of the Phoenix (film)
• Harry Potter and the Order of the Phoenix (video game)
• Harry Potter and the Half-Blood Prince
• Harry Potter and the Deathly Hallows