A teleconferencing system (1) comprises multiple teleconferencing bridges (5, 6, 7) each having an associated database (8, 9, 10). A server (20) hosts a local engine (22) associated with each bridge, and a multi-site engine (21). For a "global" conference utilising the resources of at least one other system (2), the multi-site engine (21) communicates over TCP/IP (36) with an equivalent multi-site engine of the other system to set up a link line via PSTN (31) between the bridges (5, 6, 7, 41). During the conference, the multi-site engine (21) automatically transmits event-driven updates to the remote system, and likewise receives such updates from the other system.