The Knight Bus is a triple-decker, purple AEC Regent III RT that assists stranded individuals of the wizarding community through public transportation. It operates at a very fast speed and obstacles will jump out of its way. To hail the bus, a witch or wizard must stick their wand hand in the air in the same manner that a Muggle might do to hail a taxi, though it is possible to book tickets for travel on the bus in advance.
The Knight Bus was first commissioned in 1865 as a method for underage or infirm wizards to transport themselves discreetly. The idea was proposed by then-Minister Dugald McPhail, after a number of other idea such as broomsticks with sidecars were vetoed.
Inside, during the night, the Knight Bus has beds, curtained windows, candles burning in brackets beside each bed, and thirteen Sickles buys a cup of hot chocolate, while fifteen gets a hot water bottle and a toothbrush in any colour. During the day, there are just seats that are apparently not bolted down. The bus does not seem to have much in the way of safety features, as passengers and luggage alike are being thrown around the inside of the bus during its haphazard manoeuvres.
In 1993, Harry Potter stumbled across the Knight Bus after leaving 4 Privet Drive following the inadvertent inflation of his Aunt Marge. On the same day, Madam Marsh was using the Knight Bus to travel to Abergavenny. On 20 April, 1994, Rubeus Hagrid and the hippogriff Buckbeak traveled together on the Knight Bus for a hearing in front of the Committee for the Disposal of Dangerous Creatures in regards to Buckbeak's future following the attack on Draco Malfoy. In 1996, Harry, Ron and Hermione travelled back to Hogwarts from 12 Grimmauld Place on the Knight Bus after the Christmas holidays.
The Knight Bus is named after the various night bus services throughout Great Britain, as well as a play on the word "knight", as it gives the connotation that the vehicle comes to the rescue of those who need it.
Behind the scenes
- The Knight Bus seen in the 2004 movie Harry Potter and the Prisoner of Azkaban used a body constructed from three seperate RT-class AEC Regent III buses. The triple-deck body was then fitted to a Dennis Javelin bus chassis. In order to portray the bus driving at high speeds, the cars around the bus drove slower while the bus drove at its top speed, and the footage was sped up afterward. Two buses were constructed for the film's external shots, while the interior shots were filmed on a set that would rock back and forth to simulate the bus' movement.
- One of the props is currently on display at The Making of Harry Potter. The other was moved to Orlando, Florida in 2010 for the grand opening ceremony of The Wizarding World of Harry Potter, where it carried some of the actors from the film series to the ceremony. It remained in storage until 2014, when it was moved outdoors as part of the upcoming Diagon Alley attraction. 
- The bus's height posed a challenge for the filmmakers when the vehicle was required to pass underneath bridges. To solve this problem, the top of the bus was designed to be removable.
- Since Apparition would be a faster and more practical way of transportation, the Knight Bus may be used for those who cannot use Apparition or Portkeys, and therefore need the bus, and may even be accessible to Squibs.
- In the film version of Harry Potter and the Prisoner of Azkaban, a talking Shrunken Head with a Caribbean accent was hung from the rear-view mirror.
- In the book, items appear to jump away to avoid collision. In the film, the bus just swerves around or squeezes past (or through) obstacles, and in terms of the latter, the driver is shown throwing a switch that causes the bus to contract.
- One notable feature of the film adaptation of the Knight Bus is the large chandelier hanging from the ceiling.
- In LEGO Harry Potter: Years 1-4, the Knight Bus squeezes in between two London Buses brick by brick.
- In a International trailer for Harry Potter and the Prisoner of Azkaban, Harry says to Stanley Shunpike while riding the Knight Bus: "Isn't this a bit dangerous?" to which Stan replies: "No. We haven't had an accident in about a week." These lines were cut from the final version of the movie.
- The LEGO Harry Potter Knight Bus sets are noted for their heavy use of purple bricks, which are rare and therefore much valued both for novelty and for collectors to use in their "My Own Creations."
- The Leaky Cauldron offers tickets for the Knight Bus as part of its room service.
- Concept art for the Knight Bus by Julian Caldow depicts it en route to Aberdeenshire, Cardiff, The Lizard, London, and the Isle of Skye.
- Although the capacity of the bus is not stated in the books, in the film adaptation of Harry Potter and the Prisoner of Azkaban a sign inside the bus states that the bus can carry 9 passengers, 3 on each level.
- Harry Potter and the Prisoner of Azkaban (First appearance)
- Harry Potter and the Prisoner of Azkaban (film)
- Harry Potter and the Prisoner of Azkaban (video game) (Mentioned only)
- Harry Potter and the Goblet of Fire (Mentioned only)
- Harry Potter and the Order of the Phoenix
- Harry Potter and the Half-Blood Prince (film) (Flashback on Disc 2)
- Harry Potter and the Deathly Hallows (Mentioned only)
- Harry Potter and the Deathly Hallows: Part 1 (video game) (Mentioned only)
- LEGO Harry Potter: Building the Magical World
- LEGO Harry Potter: Characters of the Magical World (Mentioned only)
- LEGO Harry Potter: Years 1-4
- Harry Potter LEGO Sets
- The Wizarding World of Harry Potter- Diagon Alley