Blood status

"But they were our kind, weren’t they?"

- Draco Malfoy asks Harry Potter about his parents (emphasis added).

Blood purity is a concept in the wizarding world that distinguishes between family trees that have different levels of magically-endowed members. It often results in prejudice towards those who have a large number of Muggles in their families. Wizarding society in general considers itself apart from and superior to Muggle society, which is not connected with magic. As Sirius Black informs Harry Potter, almost all wizards of their time have Muggles in their family trees, though some claim not to.

Muggle-Borns
"Mudblood’s a really foul name for someone who is Muggle-born – you know, non-magic parents. There are some wizards – like Malfoy’s family – who think they’re better than everyone else because they’re what people call pure-blood… I mean, the rest of us know it doesn’t make any difference at all."

- Ron Weasley explaining blood prejudice to Hermione Granger and Harry Potter.

Those born to Muggle families but who are skilled with magic are referred to as Muggle-borns. In wizarding Britain, they are allowed to attend the magical school of Hogwarts, although some other schools, such as Durmstrang Institute, only admit students with wizarding heritage. Salazar Slytherin fell out with the other Founders of Hogwarts because he wanted to limit attendance on the same grounds.

Those with prejudice against Muggles and their families often refer to such wizards as "Mudbloods", a highly offensive term implying that the individual has dirty and inferior blood. Those who discriminate against Muggle-borns believe that they do not deserve magic and should be excluded from the wizarding world, in spite of the fact that Muggle-borns are just as magically talented as those of other blood statuses.

When the Ministry of Magic fell under the indirect control of Lord Voldemort during the Second Wizarding War, it began distributing propaganda against "Mudbloods" under the authoritatorship of Dolores Umbridge. Muggle-borns were also forced to register with the Ministry's Muggle-Born Registration Commission, which accused Muggle-borns of having stolen their wands and sentenced them to Azkaban. This ended once Voldemort was defeated and the Ministry was reformed.

Half-Bloods
"Most wizards these days are half-blood anyway. If we hadn’t married Muggles we’d’ve died out."

- Ron Weasley

Wizards with families split between Muggles and wizards are referred to as half-bloods. Due to the dominance of the magic gene, children born to at least one magical parent will usually be magical themselves, meaning that a non-magical child born to a Muggle and a wizard is considered a Squib, not a Muggle.

The ancestry of a half-blood can be:
 * One pure- or half-blood parent, one Muggle parent — e.g. Lord Voldemort, Severus Snape, Dean Thomas
 * One pure- or half-blood parent, one Muggle-born parent — e.g. Harry Potter, Nymphadora Tonks, Albus Dumbledore
 * Two magical parents, at least one Muggle grandparent — e.g. Teddy Lupin

The term can be an insult, depending on the context in which it is used. Walburga Black, mother of Sirius Black, was a fervent believer in pure-blood supremacy, and screams 'filthy half-bloods' at passers-by from her portrait at Number 12, Grimmauld Place. She does this somewhat indiscriminately, which points to the mania surrounding blood purity. Bellatrix Lestrange was also insulting of Harry Potter and Severus Snape's half-blood statuses.

Some half-bloods also express prejudice against those with Muggle ancestry, despite having it themselves, often clinging to what wizarding heritage they do have. Lord Voldemort, the son of a pure-blood witch and a Muggle, epitomizes this. He hated Muggles and Muggle-borns and held his status as the Heir of Slytherin in great esteem.

Pure-Bloods
"The pure-blood families are all interrelated. If you’re only going to let your sons and daughters marry pure-bloods your choice is very limited; there are hardly any of us left."

- Sirius Black

Pure-bloods are wizards and witches with a family tree devoid of Muggle members; or, at least, they have convinced themselves of this by removing any non-purebloods from their family trees. At the very least, one must have all magical grandparents to be considered pure-blood, though extremists would require no known Muggle ancestors. Thus, some would consider the children of Harry and Ginny Potter to be pure-bloods because all four of their grandparents — James and Lily Potter, and Arthur and Molly Weasley — were wizards or witches. Others, however, would consider them half-bloods because their paternal grandmother was Muggle-born, thus they have known Muggle ancestry.

Most pure-bloods consider themselves to be akin to the royalty of the wizarding world, or at the very least the elite. They often disdain those of different blood status and Muggles, some even arguing that Muggle-borns should not be admitted into the wizarding world.

To be pure-blood is an uncommon trait. J.K. Rowling has commented that pure-blood families are the exception among wizards, rather than the rule. There appears to be a continuous stream of new families entering the wizarding world as children from non-wizarding backgrounds appear with magical ability, and as a result those with long pure-blood lines are relatively rare. To maintain their "pureblood pedigree", families such as the House of Black and the House of Gaunt have practiced inbreeding, accounting for the mental instability of certain family members. Those same families tend to disown members who accept Muggles or Muggle-born wizards into their lives. These family members would be deemed "blood traitors". For instance, the Blacks commonly blasted these relatives off the family tree tapestry.

Squibs
"Squibs were usually shipped off to Muggle schools and encouraged to integrate into the Muggle community… much kinder than trying to find them a place in the Wizarding world, where they must always be second class…"

- Muriel to Harry Potter discussing Ariana Dumbledore

Squibs are individuals from wizarding families that have not shown skill in magic. One example is Argus Filch, who is so embarrassed by this that he hides it from students and studies magic fruitlessly in his spare time. Another example is Arabella Figg, who does not seem to particularly care that she has no skill in magic. Squibs appear to keep in contact with wizarding society, whereas Muggles have little to no contact.

Squibs are generally looked upon with disdain by most wizards and witches. Even families like the Weasleys, who do not look down on Muggles or Muggle-borns, are rather embarrassed to have a Squib who works as an accountant in their family. Neville Longbottom's family was also upset at the prospect that he might be a Squib, and repeatedly tried to scare accidental magic out of him when he was a child.

Half-Breeds
"Filthy half-breeds! Beasts! Uncontrolled animals!"

- Dolores Umbridge to a group of Centaurs

Half-breeds are humans with at least one non-human parent, although witches and wizards with non-human ancestry further back would also be considered half-breeds. They are very rare, and have traits of both species, such as the ability to use magic and spell resistance in half-giants. Prejudice against half-breeds appears to be relatively common in the wizarding world, which is intolerant toward non-human peoples in general.

"Half-breed" may an insulting, rather than proper, term. It is known to be highly offensive to Centaurs, though this may only be because it is in fact incorrect; Centaurs are their own non-human breed, rather than a mix of species.

Known Half-Breed Types

 * Part-Giant — e.g. Rubeus Hagrid and possibly Olympe Maxime are half-giants.
 * Part-Veela — e.g. Apolline Delacour; her daughters Fleur and Gabrielle are one-quarter Veela.
 * Part-Goblin — e.g. Filius Flitwick is one-eighth Goblin.

Behind the scenes
There are many parallels to the notion of blood purity that exist in the Muggle world, largely in the form of racism. Examples of this being manifested include the Ku Klux Klan, discrimination against immigrants, and the persecution and mass murder of Jews, Roma, Slavs, Communists and others by the Nazis known as the Holocaust. Adolf Hitler, promoting a society with a "pure Aryan race", is believed to have a Jewish ancestor.

J.K. Rowling consciously drew such parallels: ''“The expressions ‘pure-blood’, ‘half-blood’ and ‘Muggle-born’ have been coined by people to whom these distinctions matter, and express their originators’ prejudice. As far as somebody like Lucius Malfoy is concerned, for instance, a Muggle-born is as ‘bad’ as a Muggle. Therefore Harry would be considered only ‘half’ wizard, because of his mother’s grandparents. If you think this is far-fetched, look at some of the real charts the Nazis used to show what constituted ‘Aryan’ or ‘Jewish’ blood...the Nazis used precisely the same warped logic as the Death Eaters. A single Jewish grandparent 'polluted' the blood, according to their propaganda.”''

As in the Harry Potter universe, these parallels in Muggle society have caused great strife, suffering, and cruelty in society.