Google has just announced that books you purchase from their bookstore can be read offline if you’re using the Google Chrome browser or a Chromebook.
1. Make sure you have a copy of the Google Books app. Download here.
Then, download the books in your library you want to read offline.
You can do this by moving your cursor over the cover(s) of the cover of book(s) you want to download and find the “Make available offline” checkbox in the pop-up that appears. If you’re reading a book online, you can also click the “I” in the upper-right corner of the screen.
1. You can only read ePub books offline. PDF is not supported at this time.
Additional info on this Google Books help page
See Also: Reading Google Books Offline (Android)