Our focus is the emergence of transnational administrative procedures, which we can define as an administrative procedure that leads to the adoption of a transnational decision or to regulate a transnational situation. Contrary to transnational administrative decisions or situations, that can emerge de facto, in order to have a transnational administrative procedure it is necessary to have an ex ante regulation of an administrative procedure. In these cases, the emergence of a transnational administrative situation is taken into account by two or more States and it is considered worth to be regulated. The regulation may occur through a bilateral agreement, an EU legal act, or an international Treaty. Transnational procedural principles can emerge de facto, and be discovered via case law. We propose to develop a taxonomy of transnational administrative procedures, taking into consideration e.g. the types of subjects involved, the source of law, and the type of cooperation established.