Project Gutenberg’s bookshelves are hand-curated collections of eBooks that have similar topics. Bookshelf listings were created by volunteers, and many have not been updated or may otherwise be incomplete.
Following a server upgrade in 2020, bookshelf listings are presented in the “flat” display below. Previously, there was a hierarchy, which has not yet been recreated.
Another way to find eBooks related to a topic is by browsing the Bibliographic Record section of any eBook’s page. Most have one or more selectable Subject and LOC Class entries, which take you to other books in the same category.
These are all specific bookshelves existing in Project Gutenberg.