To protect ITER from the high thermal and electromagnetic loads resulting from disruptions, prevention of such events is an essential part of the ITER plasma control system, backed up by an effective and reliable disruption mitigation system (DMS). An important aspect of the mitigation action is its trigger, the balanced decision that a disruption can no longer be prevented by scenario or stability control action and that mitigating action needs to be taken. This paper discusses the requirements for this decision process or trigger for the DMS, the expected timescales, the reliability and performance, and the possible strategy of how this may be developed for ITER high-performance operation.