A method of electronic payment for data transferred across a computer network from a server to a client by means of at least one router which forwards data. An electronic data request is sent from the client to the server via one or more routers. The server then sends electronic data to the client via one or more routers in response to said electronic data request. The electronic data is sent via a packet transfer protocol, in which each packet of data has associated with it a data field containing a value, which represents the commercial value of the requested data. Each router receives an incoming data packet, reads the value in the data field associated with the incoming data packet, calculates a new value based on the read value and the cost of forwarding the data packet, and forwards the data packet with the new value in the associated data field. Each router can check whether the value in the data field associated with the incoming data packet falls within predefined parameters and rejects the packet if the value falls outside the predefined parameters, for example if the value of the data is too high. Each router stores the accumulated value of received and forwarded data, so that payments may be made to the operator of the router.