This study is an investigation of the negotiations at the Paris Peace Conference, 1919 to make a peace in the Duchy of Teschen Silesia 1919-1920. It is concerned with the principle of self-determination as it was applied to Central Eastern Europe in the aftermath of World War I. Moreover, this investigation seeks to explain the fixing of boundary lines in the Duchy of Teschen in the light of the diplomacy of the Allied Powers on the one hand and Poland and Czechoslovakia on the other. This study is an attempt to portray the overall difficulty involved in making a peace in idealistic terms.