Hogwarts is divided into four houses, each bearing the last name of its founder: Godric Gryffindor, Salazar Slytherin, Rowena Ravenclaw and Helga Hufflepuff. Throughout the school year, the houses compete for the House Cup, gaining and losing points based on actions such as performance in class and rule violations. The house with the highest end-of-year total wins and has its colours displayed in the Great Hall for the following school year. Each house also has its own Quidditch team that competes for the Quidditch Cup. These two competitions breed rivalries between the houses. Houses at Hogwarts are living and learning communities for their students. Each house is under the authority of one of the Hogwarts staff members. The Heads of the houses, as they are called, are in charge of giving their students important information, dealing with matters of severe punishment, and responding to emergencies in their houses, among other things. The dormitory and common room of a House are, barring rare exceptions, inaccessible to students belonging to other Houses; however, different houses will share classes as they are based on year group rather than House.

In the early days of Hogwarts, the four founders hand-picked students for their Houses. When the founders worried how students would be selected after their deaths, Godric Gryffindor took his hat off and they each added knowledge to it, allowing the Sorting Hat to choose the students by judging each student's qualities and placing them in the most appropriate house. The student's own choices may affect the decision: the clearest example is the Hat telling Harry that he would do well in Slytherin in the first book, but ultimately selecting Gryffindor after Harry asks it not to put him in Slytherin.

The translators of the books' foreign editions had difficulty translating the "house" concept; in countries where this system does not exist, no word could adequately convey the importance of belonging to a house, the loyalty owed to it, and the pride taken in prizes won by the house.^[12]

Gryffindor

Gryffindor values courage, bravery, nerve, and chivalry. Gryffindor's mascot is the lion, and its colours are scarlet red and gold (maroon and gold on the ties and scarves). During the books, the Head of this house is the Transfiguration Professor and Deputy Headmistress, Minerva McGonagall until she becomes headmistress, and the house ghost is Sir Nicholas de Mimsy-Porpington, more commonly known as Nearly Headless Nick. According to Rowling, Gryffindor corresponds roughly to the element of fire.^{[citation needed]} The founder of the house is Godric Gryffindor.

The Gryffindor common room is in one of the castle's highest towers, and its entrance is on the seventh floor in the east wing of the castle and is guarded by a painting of The Fat Lady, who is garbed in a pink dress. She permits entry only after being given the correct password, as was established in the third book, when Sirius Black tried forcing entry into the tower, only to be blocked by The Fat Lady after he could not give the correct password. In the first book, Neville Longbottom tends to forget the password and must wait near the painting until other Gryffindors arrive to open the way.^[13]

Hufflepuff

Hufflepuff values hard work, patience, justice, and loyalty. The house mascot is the badger, and canary yellow and black (or golden yellow and graphite in the Fantastic Beasts films) are its colours. During the books, the Head of this house is the Herbology Professor Pomona Sprout, and the house ghost is the Fat Friar. According to Rowling, Hufflepuff corresponds roughly to the element of earth.^{[citation needed]} The founder of this house is Helga Hufflepuff.

The entrance to the Hufflepuff dormitories and common room entrance is concealed in a pile of large barrels in an alcove in the corridor that holds the kitchen. To enter, one must tap the barrel two from the bottom in the middle of the second row in the rhythm of "Helga Hufflepuff". Unlike any other house, the Hufflepuff common room has a repelling device that douses the illegal entrant in vinegar if the wrong lid is tapped or the rhythm is wrong.^[14] The Hufflepuff common room is filled with yellow hangings and fat armchairs and it has little tunnels leading to the dormitories, all of which have perfectly round doors, like barrel tops.^[15]

Ravenclaw

Ravenclaw values intelligence, learning, wisdom and wit.^[HP5][HP7] The house mascot is an eagle and the house colours are blue and bronze (blue and silver in the Harry Potter and Fantastic Beasts films and on the ties and scarves). During the books, the head of this house is the Charms teacher, Professor Filius Flitwick, and the house ghost is the Grey Lady. According to Rowling, Ravenclaw corresponds roughly to the element of air.^{[citation needed]} The founder of this house is Rowena Ravenclaw.

The dormitories are in Ravenclaw Tower, on the west side of Hogwarts. The common room is round and filled with blue hangings and armchairs, has a domed ceiling painted with stars and features a replica statue of Rowena wearing her diadem. Harry also notes that Ravenclaws "have a spectacular view of the surrounding mountains". A logical riddle must be solved to gain entry, whereas the Gryffindor and Slytherin common rooms only require a password (Hufflepuffs need to tap a barrel in the rhythm of "Helga Hufflepuff"), indicating that it may be easier for those students from other houses who possess a high degree of intelligence to enter this common room than others. Professor McGonagall, the head of the Gryffindor House, solves the riddle accurately.

Slytherin

Slytherin values ambition, cunning, leadership, and resourcefulness; the Sorting Hat said in Harry Potter and the Philosopher's Stone that Slytherins will do anything to get their way. The house mascot of Slytherin is the serpent, and the house colours are green and silver. Throughout the series, until the seventh book, the Head of House is Professor Severus Snape. Then, the previous Head of House Professor Horace Slughorn comes out of retirement, re-assuming authority after Snape becomes headmaster. The ghost of Slytherin house is The Bloody Baron.^[16] According to Rowling, Slytherin corresponds roughly to the element of water.^{[citation needed]} The founder of this house is Salazar Slytherin.

The Slytherin dormitories and common room are reached by speaking a password to a patch of bare stone wall in the dungeons, which causes a hidden door to open. The Slytherin common room is a long, low, dungeon-style room, under the Hogwarts Lake, furnished with green lamps and carved armchairs. The room is described in the second book as having a greenish glow.

The Sorting Hat claims that blood purity is a factor in selecting Slytherins, although this is not mentioned until the fifth book. There is no reason to believe, however, that Muggle-born students are not sorted there, merely that pure-blooded students are more desirable to that house, as there are several examples of half-bloods in the house – such as Snape and Tom Riddle/Voldemort – and Harry himself was only excluded from the house at his own insistence. In Deathly Hallows, a group of Snatchers claim that "not many Mudbloods" are sorted into Slytherin.

When believing Harry to be dead and thinking that he has final victory in his grasp, Voldemort proclaims his intention to abolish the other three houses and force all Hogwarts students into Slytherin. This design is foiled by his defeat and death, after which Slytherin becomes more diluted in its blood purity, no longer remaining the pure-blood bastion it once was.