This article provides a discussion about criminal insanity regulation in Norway, Sweden and the Netherlands, with a focus on the roles of legislators, judges and experts in the concretisation of the legal meaning of criminal insanity. The authors recognise that these three countries reflect different ideal type rule constructions that are interesting to study comparatively. The article addresses the following overall questions: To what extent and in what way do the different rule constructions also involve different views on the roles of legislators, judges and experts? And in case of competing models, which is the better solution? To investigate and eventually answer these questions, the authors analyse the content and legislative considerations of the relevant rules, how these rules are applied and understood by judges and experts, and how different understandings of insanity, of legislators, judges and experts, depend on each other. The authors show how the different rule constructions represent different considerations on the adequate roles of the legislator, judges and experts. They argue that what is important is not what precise division of roles that is settled, but that this interplay functions to secure clear and robust rules, and that each of the three countries has room for improvement in this regard.