From the website: ” The London Book Project is a free book exchange on a massive scale. Using the London Underground as a high speed distribution network, we aim to bring real literature to London’s commuters.
Over the next two weeks we’ll be distributing thousands of second hand books across the tube and we want YOU to get involved. If you see one of our books, please pick it up! Then read it and replace with any book of your choice. Let’s make the tube a giant, free library!”