I just tried on the Kindle Cloud Reader and was not able to copy no matter how I tried. However when I tried to open the same book using Kindle for PC I was able to copy and paste . You can download Kindle for PC here Amazon Kindle for PC Install Instructions If the book you're reading is only an azw3 format book and you can't open that with Kindle for PC you can try using Calibre to convert it to another format such as txt or html calibre - E-book management When looking up the s for this I learned that some people had trouble converting awz3 format using Calibre but simply changing the file extension to awz allowed them to fix that problem. It's worth a try. )