Abstract: Books which are to be read on portable electronic reading devices (3) are distributed to readers on pre-recorded mini-discs (2). Each book is distributed in encrypted machine readable form and has a unique identification code (28) and each reading device has a unique serial code (19). When a mini-disc is inserted into a reading device and a reader chooses a book title, the reading device transmits its serial code and the identification code of the encrypted book to a control computer (4). The control computer processes the codes to generate a decryption key (34) from the serial code and the identification code and transmits the decryption key to the reading device which is thereby enabled to decrypt the encrypted book and display the pages of the book in human readable form.