In a digital television system, a receiver/decoder (or “set-top-box”) can download one or more of several applications which can be run by the receiver/decoder to provide interactivity with the user. The applications include: an Internet browser application which uses a PSTN connection to make Internet requests and the television signal path to receive Internet responses; a shopping application operable in an “impulse” mode and a “catalogue” mode; a banking application; a quiz application which runs in synchronization with a quiz television programme; a magazine browser application; and a weather or traffic application.