As we approach the 100th anniversary of the outbreak of the First World War, students of history will revisit the causes, conduct and aftermath of the war. In each of these, Sir Eyre Crowe played a very significant role. Yet, outside academic and diplomatic circles, his name is little known. An “outsider” in the Foreign Office, he neither attended an English public school nor university. He was born and educated in Germany. Yet he rose because of his unique expertise to be the Permanent Under-Secretary from 1920 until his death in 1925, during which time he worked, not always amicably, with prime ministers and foreign secretaries such as Lloyd George, Curzon, Ramsay Macdonald and Austen Chamberlain. On his death, Stanley Baldwin called him “our ablest public servant.” Eyre Crowe was a participant in events that led to the 1914–1918 war, was one of the main organisers of the blockade of Germany, helped to end the Ruhr crisis of 1923–24, and played a major role in the acceptance of the Dawes Plan at the 1924 London Conference. Shortly before he died, he persuaded a sceptical Cabinet to accept a policy that culminated in the Locarno Pact. Yet, Crowe played a strange role at the Paris Peace Conference of 1919. Britain’s most knowledgeable expert on Germany, he was marginalised by Lloyd George prior to the signing of the Versailles Treaty, but then played a leading part as Ambassador Plenipotentiary. Crowe’s Memorandum of 1907 had a profound influence upon Foreign Office perceptions of Germany for more than forty years. The “Crowe line” on Germany was opposed by Neville Chamberlain and the British Ambassador in Berlin, Neville Henderson, prior to the Second World War. Crowe had believed that Germany was a great nation, but that Britain had made too many concessions to its government when it needed to stand firm. Foreign Office diplomats were even seen waving copies of the memorandum (by then a published document) in the faces of journalists from the pro-appeasement Times newspaper. This book focuses mainly on the 1907 Memorandum and Crowe’s career after the war, but it provides many insights into the characters, talents and failings of a number of players in this extraordinary period of history.