A method of determining the locations of a plurality of users within a predetermined space. The method comprising allocating an electronic tag having an identifier to each user, each tag being responsive to a predetermined interrogation signal to transmit a response signal from which the location of the tag within the predetermined space can be determined. The electronic tag identifier is associated with the user on allocation of said electronic tag, such that it is assumed that the location of an electronic tag corresponds to the location of the associated user. An interrogation signal is transmitted within the predetermined space and response signals are detected, to determine the location of users from the response signals.