This paper analyzes principles of international law on domestic administration with a view to their potential for codification in an EU administrative procedure law. It explains how such principles can be discovered. Subsequently, it proposes five principles: proportionality, lawfulness, non-discrimination and legitimate expectation, fairness and due process, data privacy, and transparency, information and consultation. These principles are developed on the basis of an analysis of many areas of international law such as world trade law, investment law, human rights law, refugee law, environmental law, and the law of the Sea.