There have been many reflections on the relations between the judge and the historian which have concentrated on the differences between these two figures: but what happens in cases where an historian collaborates openly with a judge as an expert consultant? What happens when an investigative office, or a court, asks an historian to reconstruct an event which is subject to a judicial procedure, or when he or she has to pronounce the ‘last word’ on an event or a document? Or, in another possible scenario, what happens when a community asks an historian to pronounce on what happened in the past, in order to ascertain which, between two contesting memories of the representation of an event, is the one which corresponds to what ‘really happened’? In these cases historians are sought out to establish the truth–their professional skills as ‘truth experts’ are called upon. And there is an extraordinary faith that the truth will be discovered. The author reflects on these issues, using as a starting point his own personal experiences as a consultant in some recent Italian war-crimes trials.