Using the three examples of port state control, green ports and ship-generated waste disposal, the article illustrates that the gateway function of seaports is also reflected in the administrative activities carried out there. The regulation of seaports is thus a typical case of international administrative law. International administrative law includes a new perspective on seaports, which not only has a descriptive-analytical added value, but also sensitises to a number of legal questions to which international law, Union law and national administrative law cannot provide answers.