There are a total of seven Harry Potter books published in the series. Their release dates are as follows:
Harry Potter and the Deathly Hallows, the seventh book in the series, was released in many countries across the world on the 21st July 2007.
The book was released in one part, the movie in two.
The Harry Potter movies are based on the books, all of which were released many years before the movies were. So yes, Harry Potter and the Deathly Hallows is a book but the book, unlike the movie, is not in two part
Harry Potter and the Chamber of Secrets was released several years ago. The book was first released on the 2nd July 1998 and the movie on the 15th November 2002.
The third book in the series, Harry Potter and the Prisoner of Azkaban.
there are many fan-written books called fan-fictions based on Harry Potter
None, all the Harry Potter books have been released.
There are many non-fiction books analyzing the Harry Potter books, but I do not think there are any released fictional books based off the series. There are, though, fan-fictions that can be as long as a regular novel based off of the Harry Potter series.
Nothing because Deathly Hallows was the last Harry Potter book and Voldemorts dead and stuff. But if there is book about Percy Jackson and Harry Potter meet each other. That will be awesome!!
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Given that, in the UK, only the first two books had been released and that the first book was just being released in the US, not many. However, accurate sales figures are very difficult to get for the early Harry Potter books.
depends on the book, but mainly it is usually harry Ron and Hermione :)