This thesis aims to elaborate the Mosul question, which was dispute first between the Great Britain and the Ottoman Empire and later between the Great Britain and Turkey. It attempts to analyze the resolution process of the Mosul question as a result of a very complex process between the years 1918-1926, with various political, diplomatic, military and legal dimensions by taking the fact into consideration that the Great Briatin was the strongest member of the League of Nations, but Turkey was not even a member.