This thesis considers how attitudes shaped British, French, and American policy regarding the rebirth of Poland. From the outbreak of war in 1914 to the plebiscite in Upper Silesia in 1921, Allied and American policy-makers first considered whether Poland should be an independent state and then where its borders should be. As they did this, they developed attitudes about these questions, for instance about Poles and the right or ability of the Polish nation to administer a modern state. Such considerations assumed that national character exists and is important in the success or failure of a country. My research draws on literature from social psychology in defining the development of such understandings as consistent with stereotyping, in other words using generalisations about social groups to understand those groups or individuals. Allied and American policy-makers considered Poles to be, for instance, quarrelsome, aggressive, anti-Semitic, pitiable, passionate, or loyal. The thesis begins by examining pre-war attitudes to Poland and the impact of the war on these and on the diplomacy of the Polish question. It then discusses the re-emergence of an independent Poland in 1918 and the impact on policies and attitudes of the Polish delegation’s claims at the Paris Peace Conference, of events on the ground, and of the Russo-Polish War. Allied and American decision-making on the rebirth of Poland was central for European diplomacy not only because the attitudes they expressed left lingering grudges on both sides, but also because Poland’s frontiers were an irritant throughout the interwar period until Germany and Russia invaded Poland in September 1939. Moreover, the conclusion that attitudes were a factor in decision-making contributes to a growing recognition among international historians and international relations theorists that it is necessary to look beyond individuals' 'rational' motivations.