The Fan Fiction Studies Reader Paperback – Illustrated, February 15, 2014

Great introduction to the field.

If you want to read something new about the topic, there's the introduction, otherwise they're all extracts from other books, cut-out as the editors pleased. If you want a list of must-read books about the topic, you might just want to browse the contents page, write down the titles and authors, and read those in their entirety. Recently I've consulted it for the introduction only, to be honest.