Abstract: Event processing apparatus for processing electronic tag reading events comprising a first event processing module and one or more second event processing modules. The or each second event processing module is operable to receive event data records concerning electronic tag reading events from electronic tag readers, and to transmit to the first event processing module processed event data records concerning selected electronic tag reading events. A filter control module transmits filter definitions to the second event processing modules and subsequently transmits filter control signals indicating that filters should be activated or deactivated in order to avoid overloading of the first event processing module. Statistics concerning the selectivity of filters, including filters which are currently inactive, are used to determine which filters should be activated or deactivated.