NATO has been a fixed point in international politics for forty years and is part of the basic framework of relations between the West and the Soviet Union. NATO present form owes much to the milieu of the late 1940s which gave it birth and to crucial developments in its early years. Important insight into the character of the alliance can be gained by examination of the negotiation of the North Atlantic Treaty itself. It has emerged from recent scholarship that those who created the Treaty were at variance not only on the details of the Treaty, but also on the fundamental nature of the alliance they were creating: its purpose, and the means by which it could best achieve that purpose. Important studies have highlighted the debate upon the issue of the obligation to assist a member if attacked (Article 5 of the Treaty) and the mutual assistance clause (Article 3). The debate on membership of the Atlantic Pact, and particularly the criteria to apply when assessing potential members also raises fundamental questions but it has been less exhaustively studied. There is especially a lack of detailed study of the development of British views, which were of some importance given the pivotal initiatory role the British played in the negotiations, now widely recognized. The British official documents reveal not only the development of ideas on aspects of the North Atlantic Treaty in debate within the British government, but also provide much information on the course of the Treaty negotiations and the views of the other participants, to supplement that available in the published sources. This information results from the close contacts between the British Embassy in Washington and the State Department, and Britain's close ties with the West European participants through the Brussels Treaty organization.