Hogwarts birth register

The Hogwarts birth register was a large, parchment book at Hogwarts School of Witchcraft and Wizardry, in which the Magical Quill wrote down the birth of every magical child.

Use
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 Second Wizarding War.

Behind the scenes

 * It is assumed (though not explained) that this book only records magical births within the United Kingdom.
 * It is unknown why Professor McGonagall is the one to check the book, possibly due to her status as Deputy Head (and later Headmistress).
 * It is not known if this tradition of tracking magical births with the Quill existed prior to McGonagall's career at Hogwarts, whether it was her idea/replacement for an older system or even if it continues to be used after her retirement.
 * On Pottermore.com, the Magical Quill will be used as a way to register people on the website early, starting on July 31st, 2011, and ending on August 6th, 2011. People will have to to solve a riddle on the homepage and add 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 answer the riddle correctly, then they have "found the Magical Quill" and are allowed to register for the website prior to the scheduled public launch on October 1st, 2011. There will be seven riddles, one each day for the duration of the week. Each one will be about one of the different Harry Potter books. Day one's riddle will be about Philosopher's Stone, day two's about Chamber of Secrets, and so on. The riddles will become progressively easier as the week goes along, with the riddles for the first three days being more difficult than those for the last four days.
 * It is possible that this book and the book containing a list of Hogwarts students are one in the same. They are similar in appearance.

Appearances

 * Harry Potter and the Philosopher's Stone (film)
 * J.K.Rowling Official Site
 * Pottermore