With more than 40,000 items, the Grosvenor Rare Book Room includes numerous and varied holdings in both subject and format. One of the most fascinating are the more than 300 miniature books held within the collection. Generally, miniature books must be smaller than 3 inches measured in each direction. However, some collectors argue there are four types: Macro-mini, between 3 and 4 inches tall, Miniature, between 2 and 3 inches tall, Micro-mini, between 1 and 2 inches tall, and Ultra-micro-mini, less than 1 inch in total.
At first, miniatures were made for convenience; they could be carried in a pocket or tied to the waist. Later, books of this size were created as a challenge for bookbinders and printers, allowing for experimentation in bindings, coverings, illustration, and typography. Miniatures can be of any subject and genre, and are often made the same way as standard books, for example, with a sewn or glued binding, letterpress text, calligraphy, lithography, or engraving. They can also be pop-ups, foldouts, or even scrolls. Rare Book Room holdings include examples of illustration, reference works, children’s books, religious texts, literature, songsters, local interest, and books about books.