My title, which is stolen from a collection of learned German essays edited by Ernst Käsemann (Das Neue Testament als Kanon, 1970), may sound remote from the concerns of the practical ministry. But the academic question here raised has profound implications for all our understanding, proclamation and practice of the gospel. My exposition will fall into three parts. First I shall make clear what, historically, were the theological motives governing the establishment of a fixed canon of New Testament scripture, and I shall discuss the question of how far the aims of the early Church in this matter may be considered, in the light of modern critical scholarship, to have been achieved. Next I shall show that today also we are faced by problems similar to those which the principle of a New Testament canon was designed to meet, and I shall try to indicate what part the canonical New Testament may still play in helping us to meet them. Thirdly, I shall draw some consequences for worship, preaching, evangelism, ecumenism, and ethics from the principle of a New Testament canon and from the actual content of the canonical New Testament. In conclusion, I shall briefly consider the place of the canonical New Testament in the problem posed by the particularity of Christianity's historical origins and the universality of its claims. Space will obviously forbid anything more than the giving of hints on all these questions.