Electronic payment authorisation using a mobile communications device

A system for authorising payment for retail transactions by credit cards or the like comprises at least one merchant terminal (1), such as a point of sale terminal or a "cardholder not present" terminal, linked to a card issuer's transaction processing unit (2). An authorisation module (3) linked to the processing unit (2) compares data for a transaction with preset criteria, such as a transaction threshold value or a location of use of the card. Authorisation of the transaction may be suspended as a result of this comparison. A message generation module (4) then produces a notification of the transaction which is sent via a transmitter (5) to a preselected mobile telephone (6), PDA or the like. The mobile telephone (6), etc, is used to send confirmation of the transaction back to the authorisation module (3), which then allows the transaction to be completed. In the absence of such confirmation, the transaction is cancelled.