Abstract: A data processing system comprises a plurality of electronic book reader devices, each of the electronic book reader devices having a display and being connectable to a wireless network of electronic book reader devices, in which: a first electronic book reader device of the plurality comprises a data transmitter configured to send, via the wireless network, reading position data defining: a current book data file being displayed by that electronic book reader device, and a current display position within that book data file; and at least a second, different, electronic book reader device of the plurality comprises a data receiver configured to receive, via the wireless network, the reading position data sent by the first electronic book reader device, and a display controller configured to control the second electronic book reader device to display at least an indication of the current book data file and the current display position of the first electronic book reader device.