The Hogwarts Library "contains tens of thousands of books on thousands of shelves." . 

It was described in the Harry Potter books about the life of the famous wizard, Harry Potter, as:- "And then, of course, there was the sheer size of the library; tens of thousands of books; thousands of shelves; hundreds of narrow rows." .

That should give you an estimate of how huge and spacious the Hogwarts Library is, and how big the collection of books in it must be.

In the times of Harry Potter, the famous wizard, it was overseen by the British witch Madam Irma Pince, who was a strict librarian and a loving protector and guardian of the books in the Hogwarts Library, though she was rumored to have been not very helpful to students in searching and finding the books they needed for making research on additional information for homework and other purposes in the Hogwarts Library, because of her demeanor. She was also rumored to breathe down the necks of the students reading books in the Hogwarts Library from behind. However, overall, in my opinion, a strict librarian makes for a good guardian for the books and their knowledge in the Hogwarts Library.

The Hogwarts Library has a separate Restricted Section at the back of the library, which houses dangerous books and books associated with dark magic. It can only be accessed with special permission from the Hogwarts Professors or the Hogwarts Headmaster. 

The Hogwarts Library has a lot of interesting history to it's name, only a small part of which is about housing the Vault of Fear behind one of the bookshelves in the Restricted Section of the Library, which once unleashed a great number of boggarts, releasing them around the school. To know more interesting history about the Hogwarts Library, you will have to do a lot of research on your own.

The current Hogwarts Library is very huge, spacious and expansive with a large collection of books on various topics, written, updated, edited and/or reprinted and published by many different witches and wizards, Hogwarts students, Hogwarts Professors and Hogwarts staff alike. It houses everything from textbooks to reference books to academic material and study notes to books containing important information to published diaries and/or adventure logs of students and staff at Hogwarts to novels with all possible different types of plots and of all possible different genres containing fictional or true stories.

In the current Hogwarts Library, there is no librarian, however, the library is overseen by Headmistress Oshiro, and you can owl her with queries in case of any problems. The current Hogwarts Library also has a plethora of strict rules to be followed, all of which are to be found listed and explained in the book written and published in the current Hogwarts Library by Headmistress Oshiro, titled, "The Guide to the HiH Library" , and some of which will be discussed in this book. The current Hogwarts Library is also monitored by Hogwarts's own inherent magic and you can find yourself in trouble if you don't follow the rules and regulations of the Hogwarts Library, as mentioned in the book , titled, "The Guide to the HiH Library" by Headmistress Oshiro.

The current Hogwarts Library also has a Restricted Section which houses books inappropriate for underage readers or books with A rated content or dangerous books or books with information on very dark magic. The Restricted Section of the current Hogwarts Library is not visible to you and you cannot access it without express permission.