One of the least-known and certainly least-celebrated measures of arms control to be negotiated since the Second World War is the 1971 treaty prohibiting the emplacement of nuclear weapons on the seabed. Admittedly, it is not one of the more significant agreements of its kind, being a preventative “non-armament,” rather than a true disarmament measure, and relating to weapons which, although technically feasible, are not at present thought to be of any great military value. Nevertheless, it is important. At least one measure of the treaty’s significance is its role as a first step towards a more comprehensive demilitarization of this vast, new environment — the terrestrial analogue of outer space — which is only beginning to be opened up to human exploration and exploitation. The seabed, including the continental margin1 as well as the so-called “deep ocean floor,” covers no less than seventy per cent of the earth’s surface, or about one hundred million square miles.