Recommended Reading List
To understand a lot of the references in the Harry Potter series, I have (with the help of The Ultimate Unofficial Guide to the Mysteries of Harry Potter) compiled this list of recommended reading, in case you have a few spare years (I myself have read only about half of this list):

The Hobbit and The Lord of the Rings by J.R.R. Tolkein

Chronicles of Narnia by C.S. Lewis

Wizard of Oz series by Frank L. Baum

Alice's Adventures in Wonderland and Through the Looking Glass by Lewis Carroll

the complete works of William Shakespeare

Nancy Drew mysteries by Carolyn Keene

Jane Austen's novels

The Iliad and The Odyssey by Homer

Mythology by Edith Hamilton

The Little Giant Encyclopedia of Superstitions by the Diagram Group

Fantastic Beasts and Where to Find Them and Quidditch Through the Ages (available through Scholastic)

*Not reading necessarily, but it's good to have a dictionary on hand.
*Comprehensive knowledge of the various incarnations of "Star Trek" is also helpful (goblins have been likened to the Ferengi of "Deep Space Nine").
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