Four British Fantasists: Place and Culture in the Children's Fantasies of Penelope Lively, Alan Garner, Diana Wynne Jones, and Susan Cooper, Charles Butler (Rowman & Littlefield, 2006)
The Wand in the Word: Conversations with Writers of Fantasy, Leonard Marcus (Candlewick, 2006)
Other websites
Wikiquote has a collection of quotations related to: Susan Cooper
The Lost Land of Susan Cooper – official website with links to articles and interviews available online, at "About Writing for Children"