Abstract: Each terminal in a full-duplex communication system comprises a computer-controlled display screen such as a CRT, at least one input means such as a keyboard, a mouse or a light pen and bidirectional communication means through which the terminals are interconnected. Each communication means comprises a receiver for receiving display information received at the terminal from the remote terminal(s) and a transmitter for transmitting information to the remote terminal(s) where it is displayed. In accordance with the invention, each terminal also comprises control means which periodically read sits input means and communications means and uses the information contained therein to control the content of its display. Further, the control means at each terminal also provides to its transmitter instructions which are transmitted to the remote terminal to change the display at the remote terminal so that all the displays are the same.