The Pure-Blood Directory is a small, black-bound book discovered by Hermione Granger in the library of 12 Grimmauld Place. The title is printed on its cover. It was one of many dark and questionable books in the Black family's collection, reflecting their obsession with blood purity.
The primary function of the Pure-Blood Directory is not magical in nature but ideological. It serves as a registry of wizarding families that the anonymous author deemed to be “truly” pure-blood by the 1930s. The book was intended to help such families maintain their blood purity by encouraging intermarriage only with other families on the list.
Published sometime in the early 1930s, the Pure-Blood Directory was an attempt to codify the notion of blood purity in Great Britain. The anonymous author, widely speculated to be Cantankerus Nott (Pottermore), established a set of criteria for inclusion that many in the wizarding community found dubious and arbitrary. Families like the Potter family were deliberately excluded because their common surname suggested possible Muggle origins and because they had historically advocated for Muggle rights (Pottermore). The Gaunt family, despite their immense pride in descending from Salazar Slytherin, were known to doubt the purity of every family but their own. The families listed in the directory, known as the “Sacred Twenty-Eight,” are as follows (Pottermore):
A copy of the book remained in the Black family library for decades. In August 1997, Hermione Granger found it while searching for books about Horcruxes at 12 Grimmauld Place and mentioned it to Ron Weasley. Ron confirmed his family's inclusion, stating, “The Pure-Blood Directory… a list of the twenty-eight truly pure-blood families… My family's in there… we're related to the Abbotts and the Longbottoms and the Crouches…” He also noted his mother's desire to be blasted off the Black Family Tapestry for being related by marriage to a Weasley.
While a minor object, the Pure-Blood Directory is a significant piece of world-building that illustrates the deep-seated prejudice within the wizarding world. It serves as tangible evidence that the ideology of blood purity championed by Lord Voldemort and his Death Eaters was not a new concept but a long-standing and institutionalized form of bigotry. Its discovery in Harry Potter and the Deathly Hallows provides immediate context for the Second Wizarding War, reminding the trio and the reader of the societal divisions they are fighting. The book underscores the hypocrisy and arbitrary nature of blood status prejudice, as seen with the inclusion of families like the Weasleys who opposed the idea, and the exclusion of families like the Potters.