In a three day trial in April 2008, the United States District Court for the Southern District of New York considered whether the Harry Potter Lexicon infringed the intellectual property rights of J.K. Rowling and Warner Brothers. The case has attracted great media attention. As John Crace, a reporter for The Guardian, observed: “On one side: global-celebrity author J.K. Rowling. On the other: an amateur fan site devoted to the world's favourite boy wizard. At stake: the soul of Harry Potter.”

J.K. Rowling is the author of the seven book Harry Potter series, which tell the story of a young wizard, Harry Potter, and his battles with Voldemort, the Lord of Darkness. As the court papers noted, “The Harry Potter Books are a modern day publishing phenomenon and success story.” Warner Brothers sought and obtained the film rights to the series. The entertainment company has thus far produced five films; a sixth is due in November 2008; and the final instalment is planned.

The Harry Potter Lexicon is a reference guide created by Steven Vander Ark, a former grade school teacher. He has organised a large volume of material on the Harry Potter books and the Harry Potter films on a website in an alphabetical listing, from “A-Z”. The founder of RDR Books, Roger Rapoport, approached Ark to publish the Harry Potter Lexicon in a book form. Ark agreed to this request, and provided the publisher with a condensed version of the web-site.

After RDR Books announced its intention to publish the reference book, J.K. Rowling and Warner Brothers brought a legal action in the United States District Court for the Southern District of New York, alleging that the publishers of the Harry Potter Lexicon were in breach of various intellectual property rights. A spokesperson for Warner Brothers and J.K. Rowling observed:

"A fan’s affectionate enthusiasm should not obscure acts of plagiarism. The publishers knew what they were doing. The problem remains that the Lexicon takes an enormous amount of Ms. Rowling’s work and adds virtually no original commentary of its own. As we’ve said in court, it takes too much and adds too little. Authors have a duty to prevent the exploitation of their works by people who contribute nothing original, creative or interpretive."

The litigation involves the intersection of copyright law, trade mark law, and consumer protection law. It has a wider significance because it deals with the protection of authorial rights; the use of literary indexes, supplements and reference guides; and the clash between character merchandising and fan fiction.