Sir Horace Wilson was Neville Chamberlain's confidential adviser while the latter was prime minister. The article addresses three questions. First, what was Wilson's role in Whitehall in connection with rearmament and foreign policy? Second, did he diminish the influence of the Foreign Office? Third, what contribution does his defence of appeasement make to understanding of a subject that continues to divide historians? The article concludes that Wilson played an important role in enabling Chamberlain to pursue his foreign policy goals. However, when there was outright disagreement between Wilson and the Foreign Office, it was the Foreign Office view that prevailed. Finally, the evidence of Wilson's words and actions, both in 1937–9 and later, broadly supports R. A. C. Parker's post-revisionist interpretation of appeasement, particularly as regards Munich, but Wilson was a good deal firmer in 1939 about Britain's will to fight, if necessary, than his critics then or later allowed.