This section explores yet another way in which – sometimes – the vague negligence standard of reasonableness can be supplemented: negligence per se. In those rare (and happy?) occasions in which a rule of behavior is laid down by the law – for the purpose of safety, and perhaps as part of the criminal canon – we see courts willing to adopt the law itself as the standard of care. When this is done, it does not merely provide a basis for inference as res ipsa does, but rather substitutes for the standard itself. If the conditions for NPS are met and the law can be shown to be broken, the defendant is liable (or, if contributory negligence is claimed as the candidate for NPS, the plaintiff’s case is lost). The cases here provide good examples of when the doctrine works – and when exceptions to its application are sought and granted.