The United Nations General Assembly has recently appealed to all countries to “refrain from taking any action directed at undermining the [law of the Sea] Convention or defeating its objects and purposes”. The Convention on the Law of the Sea made at Montego Bay in September 1982 took nine years to write following five years of preparatory work and covers all the major law of the sea issues; resource exploration and exploitation, navigation and overflight, conservation and pollution, fishing and shipping. The Convention has not yet entered into force and it may be some time before it does so. During that time existing international law will be augmented along the Convention lines by the national legislation of states seeking to safeguard their interests while the Convention remains inchoate. Although the aforementioned Resolution is non-binding and of recommendatory value only, it does appear to stress an existing rule of international law which has something to say about the conduct of states which have signed the Law of the Sea Convention prior to its entry into force. Article 18 of the Vienna Convention on the Law of Treaties requires that a nation, after signing a treaty, refrain from “acts which would defeat the object and purpose of a treaty” until such time as the nation indicates its intent not to ratify. The extent of the duties incumbent upon states as a result of this obligation is unclear, but the General Assembly Resolution is perhaps evidence that, as time progresses without the entry into force of the Convention, the obligation shall play a significant role in the regulation of the conduct of signatory states towards the Convention in many of the diverse areas with which it is concerned. The object of this article is to analyse one particular area of the Convention, that of the regime for the mining of the resources of the International Seabed Area under Part XI of the Convention. This throws into relief the problems which signatory states may face as they seek to legislate or take action to secure rights and to comply with duties under a Convention which is not yet in force. It may be that the citation of the duty not to defeat the object and purpose of the Convention is far more problematic in terms of a successful outcome to the negotiations than at first appeared.