The 'Noble and Most Ancient House of Black' is one of oldest pure-blood wizarding families. The ancestral home of the Black family is in London, at Number Twelve, Grimmauld Place.

From the Story

Harry Potter and the Order of the Phoenix

Discovered in chapter 6, The Noble and Most Ancient House of Black

Many other pure-blood families are distantly related to the House of Black. Most members of the Black family supported Voldemort's ideals of purification of the wizarding race, getting rid of Muggle-borns and placing pure-bloods in charge, although they got cold feet when they saw what the Dark Lord was prepared to do to gain power. Regulus Black, Sirius's brother, became a Death Eater. The Black family includes Phineas Nigellus, the least popular Headmaster Hogwarts ever had; Araminta Meliflua, who tried to force through a Ministry Bill to make Muggle-hunting legal; and Elladora, who started the tradition of beheading house-elves when they got too old to carry a tea tray.