This article analyses, from historical and comparative perspectives, three closely related concepts of administrative law – namely records, reasons and rationality. It finds that the concept of the ‘administrative record’ is far more significant in United States administrative law than in either English or Australian administrative law, and suggests why this might be so. The importance of the record in US law explains why it imposes stronger obligations on administrators to give reasons than does either English or Australian law. It also explains why terms such as ‘rationality’ and ‘reasonableness’ have significantly different meanings in US administrative law on the one hand, and English and Australian law on the other.