The eventual product of the International Law Commission's (ILC) work on state immunity hasbeen in the form of a Convention. This prompts the question whether widespread ratification (or accession etc) will be necessary for clear rules of international law on state immunity to become firmlyestablished or whether a substantial codifying effect could be achieved even if the Convention does not attract a great number of parties. The latter has sometimes been said of much of the Vienna Convention on the Law of Treaties. As the law on state immunity has undergone much of its substantial development by practice of national courts (albeit that the piecemeal adoption and implementation of treaties has played some part), could this process not simply continue with the Convention providing guidance or a model? If the trend from absolute to restrictive immunity could occur by development of customary law, are there not still adequate means of consolidating customary law without the need for states actually to become parties to the treaty?