Apparition

Apparition is an advanced spell used by fully trained witches and wizards to disappear from one place and appear almost instantly somewhere else. A person who uses this spell is referred to as an Apparator. Apparition is typically cast non-verbally.

• No one can Apparate or Disapparate inside Hogwarts because of magical protections, according to Hogwarts, A History and also Professor Snape (PA6,PA22)
• A house-elf can Apparate or Disapparate almost anywhere. Dobby was able to get into Harry’s bedroom on Privet Drive then Disapparate “with a crack like a whip” (CS2), and appear and disappear inside Hogwarts (CS10). Kreacher somehow escaped the sea cave (DH10), and brought Mundungus Fletcher into Grimmauld Place with side-along Apparition (DH11).
• Underage Apparition is tracked by the Ministry via the Trace, according to Mad-Eye Moody (DH4)
• Very difficult spell. Performed incorrectly, Apparition can result in the caster being “splinched”, which refers to part of the caster’s body being left behind (GF5, DH14). According to Harry’s Apparition instructor, this happens when the caster is insufficiently determined (HBP18).
• According to Harry’s Apparition instructor, there are three D’s in performing Apparition: destination, determination, and deliberation. (HBP18).
• Wizards must pass a test in order to be obtain a license to be allowed to perform it. To take the test, the applicant must be of age in the wizarding world (at least seventeen) (HBP4).
• Apparition becomes more difficult as distance increases. Only highly trained wizards would try intercontinental Apparition (QA9). According to the WOMBAT Test there may even be a law against it (JKR-W3)
• Fudge appeared out of thin air in the cabinet room to inform the Prime Minister of the goings-on at the Quidditch World Cup (HBP1).
• Apparating directly into a Wizarding house is just as rude as kicking down the front door, even if most Wizarding dwellings were not magically protected from unwanted Apparators (HBP4).

References from the canon

• The first mention of Apparition in the books is in CS5. Ron tells Harry that his parents don't need the Ford Anglia to get home because they can Apparate there. Harry learns more details about Apparition in a conversation with the Weasleys about traveling to the Quidditch World Cup (GF6).
• See PS2 for a possible example of Apparition as wandless magic. However, given Harry's remarks in (HBP4) that his experience at that time was the first time he had ever Apparated, it would appear that the incident referred to in PS2 was probably not Apparition but something else, such as Levitation.
• See also Side-Along APPARITION and OP - Edits and Changes to the Text.
• Pius Thicknesse made it an imprisonable offence to connect number four, Privet Drive to the Floo Network, place a Portkey there, or Apparate in or out, supposedly to protect Harry (DH4). So the Order used the Seven Potters plot with Polyjuice Potion and brooms to get Harry to safety.
• According to Remus Lupin, it's impossible to track anyone who Apparates, unless you grab hold of them as they disappear (DH11).
• Harry, Ron, and Hermione Apparated together throughout what would have been their seventh year many, many times, beginning with their escape from the wedding (DH9). Harry never took the Apparition Test after he turned 17, and Ron took it once and failed (HBP22).
• Harry and Hermione practiced Apparating and Disapparating together under the Invisibility Cloak (DH16).