Abstract: An electronic trading system is disclosed for principally for trading in intangible things, particularly financial instruments. The trading system comprising a quality-of-service (QoS) subsystem, which subsystem is operative to impose limitations upon trading activities in order that the performance of a component of the system or of the system as a while is maintained within specified tolerances. For example, it may limit the number of events that can be initiated by a trader. It may also allow some messages to be routed through the system with a priority that is higher than others when such messages have a particular content (e.g. are inherently urgent in nature or essential to proper operation of the system) or are to or from a privileged user. The system also has an integrated protocol stack for routing of data to enable the location of data bottlenecks to be identified.