Abstract: A monitoring system 10 is provided which includes a primary electronic tag 12, a secondary electronic tag 16, reading apparatus 20, and a comparator 26. The primary electronic tag 12 includes primary identification data associated with the primary bearer 14 of the tag 12 and the secondary electronic tag 16 includes secondary identification data. The secondary identification data is associated with a secondary bearer 18 of the tag 16 and is also associated with the primary identification data. The reading apparatus 20 remotely reads the primary and secondary identification data and the comparator 26 compares the data and generates an output signal dependent upon the outcome of the comparison. The invention extends to a primary electronic tag 12 for use in monitoring movement of at least one secondary electronic tag 16. The invention also extends to a method of monitoring movement from a selected zone and a method of monitoring the use of at least one vehicle.