Online Harry Potter fans transformed what it means to love a story.

Through their remarkable ubiquity, J.K. Rowling's series and the films based on it shaped an entire generation to an unprecedented and still unreckoned-with degree. Earlier touchstones-the Beatles or Star Wars, for example-may have marked epochal cultural moments, but Pottermania united kids across the globe, pulled in vast numbers of adult enthusiasts, and enjoyed the whole-hearted support of a well-coordinated and highly effective network of professionals-teachers, librarians, and booksellers among them. Certainly book publishing, usually regarded as a sleepy backwater of the culture industry, had never seen anything remotely like Harry Potter before (or since). Everything about the general frenzy, from the seemingly endless stream of media coverage to the hundreds of people lining up for midnight bookstore parties, came as a revelation.