The Interstitial Library’s Circulating Collection specializes in interstitial books, defined as:
Books that fall between categories recognized by other libraries.
Books that occupy cultural blind spots, because they are deemed to be offensive, trivial, unfashionable, or to contain false information.
Books that are notable for qualities not catalogued in ordinary libraries, including those ordinarily seen as extrinsic to the text—e.g. intriguing marginalia, provocative typos, a rare butterfly crushed between two pages.
Books that do not exist in ordinary terms—e.g. fictional books, books that have been lost or destroyed, books that are yet to be written.