Is it possible to get a book category based on ISBN?
The Google Books API offers a category-field.
Example: https://www.googleapis.com/books/v1/volumes?q=isbn:055380457X (Business &amp; Economics being the category).
Another example would be WorldCat. Just type in the ISBN in the search for books, and you will find categories or topics associated with that book. (They also have a machine-readable API, but you will need to register, as far as I know.)
But note that normally every library uses its own curated hierarchy of tags.