The policies of the so-called great Powers toward China in the twentieth century have frequently given rise to serious diplomatic disputes. Fortunately, in many cases, these differences have tended to clarify conflicting interpretations of policy, and by so doing have led to a better understanding of principles on which more complete agreement might be achieved. Conspicuous among such cases is the policy usually referred to as the Open Door. From 1899 until 1922 the Open Door in China was a subject of almost constant international friction, due, in part, to a lack of common agreement as to the precise commitments to which the Powers were pledged. Specific cases of disagreement led finally to a better appreciation of the principles involved, and in 1922 the Open Door policy was given its first treaty definition. The following pages are an attempt to analyze a series of events in 1916-17 which demonstrated the wide gulf between American and European interpretations of the Open Door, and the imperative need of a new definition of the policy. The essential background of the discussion may be stated briefly.