The Book of Admittance was a large, parchment book bound in black dragon hide at Hogwarts School of Witchcraft and Wizardry, in which the Quill of Acceptance wrote down the birth of every magical child. A powerful magical artefact in its own right, the book served as a regulatory system, refusing to allow the quill to write in it until sufficient evidence of magical ability was displayed, thus guarding against Squibs being incorrectly admitted.
As this record contained the name and birthdate of every magical child, it was used to tell who was eligible to attend Hogwarts, and when. Every year, Professor Minerva McGonagall checked the book and sent acceptance letters by owl to children who were close to turning eleven, letting them know of their place at the school. Additionally, for Muggle-born children, "special messengers" were sent to personally explain the wizarding world to their parents.
The Ministry of Magic did not have its own means of detecting magical births and did not not have access to the Hogwarts birth register. This is presumably why the creation of the Muggle-Born Registration Commission was necessary for the Ministry to determine who was Muggle-born and persecute them accordingly during the Second Wizarding War.
Behind the scenes
- It is assumed (though not explained) that this book only records magical births within the United Kingdom and probably Ireland.
- It is unknown why Professor McGonagall is the one to check the book, possibly due to her status as Deputy Head (and later Headmistress).
- On Pottermore.com, the Magical Quill was used as a way to register people on the website early, starting on July 31st, 2011, and ending on August 6th, 2011. People solved a riddle on the homepage and added the answer to the riddle to the end of the URL http://www.quill.pottermore.com/ to obtain a chance at early registration for the site. If they answered the riddle correctly, then they had "found the Magical Quill" were granted access to the website prior to the scheduled public launch on October 1st, 2011. (delayed until the ides of February) There were seven riddles, one for each day of the competition week, each one about one of the different Harry Potter books. Day one's riddle was about Philosopher's Stone, day two's about Chamber of Secrets, and so on.
- Harry Potter and the Philosopher's Stone (film) (First mentioned)
- J.K.Rowling Official Site