This thesis, the first study of Nevile Henderson to be completed at doctoral level in the UK, takes a fresh look at Henderson's controversial role in Berlin between 1937 and 1939. It begins by re-examining Henderson's controversial appointment to the Berlin Embassy, and contends that a close study of his earlier career (especially in Belgrade between 1929 and 1935) help to explain those aspects of his behaviour that gave rise to criticism. After close analysis of published and unpublished Foreign Office documents, the thesis challenges the traditional view that Henderson favoured the Anschluss and the dismemberment of Czechoslovakia in 1938. It also re-examines the charge that he undermined British policy by making indiscreet remarks in Germany, and argues that his scepticism about the anti-Nazi opposition was fully justified. And that he did, to a degree, carry out his 'warning' function in Berlin. Another key aspect concerns the extent to which Henderson's line in Berlin had support in the Foreign Office, and the re-consideration of his pivotal relationships with Chamberlain and Halifax. Particular attention is paid to the decision to send Henderson (by then a seriously ill man) back to Berlin in February 1939. The author's overall view is that, given Henderson's flawed analysis of the Nazi regime, a totally revisionist analysis of his time in Berlin would be untenable. The main conclusions are (a) that Henderson's influence on British policy has been exaggerated and (b) that he has been unfairly treated by historians. This thesis seeks to redress the historical balance by presenting the first close analysis, and rounded account, of what Henderson called the 'failure of a mission'.