By default, the iBooks app has two statuses for books: "new" and "not new." A new book is marked with a blue "New" tab across the top right corner of its icon but this disappears the moment a page of the book is turned; making being able to distinguish between read and currently reading books difficult. As a result, knowing how to mark a book as read in iBooks is not simply a matter of reading it.
Open iTunes. Click the "File" menu and select "New Smart Playlist." Alternatively, press "Alt," "Cmd" and "N" (at the same time) to open the "New Smart Playlist" dialogue box. This begins the process of creating a new playlist that filters its own contents on your behalf and will only contain unread books. Ensure the "Match the following rule" box is ticked.
Click the "Artist" drop-down box and scroll down. Select "Playlist." The next two drop-down options turn to "is" and "Music," respectively. Click the "Music" box and scroll down. Select "Books." The first rule in your new "Smart Playlist" is now set. Click the "+" button. This begins creating the second rule.
Click the "Artist" drop-down box and scroll down. Select "Plays" this time. The next two drop-down options turn to "is" and "0." Leave these alone, as the rules are now set correctly for the playlist to only include unread books. Click "Okay." The playlist name is highlighted in the left sidebar. Enter the name "Unread books" and press "Return."
As an alternative to creating a smart playlist, open iBooks and create a new "Category" called "Unread books." Press the "Edit" button and select each book you have not yet read. Press the "Move" button and select the "Unread books" category. The books are now moved into the new category.
The unread books smart playlist only updates when the "Live update" option is checked on the "Edit Smart Playlist" dialogue box, so be sure that this remains checked when you create the smart playlist. Furthermore, be sure to sync your copy of iTunes with the device you read iBooks on, otherwise data will not be available for the smart playlist to update itself.