Reciprocity (international relations)
（重定向自Reciprocity principle）
In international relations and treaties, the principle of reciprocity states that favours, benefits, or penalties that are granted by one state to the citizens or legal entities of another, should be returned in kind.
For example, reciprocity has been used in the reduction of tariffs, the grant of copyrights to foreign authors, the mutual recognition and enforcement of judgments, and the relaxation of travel restrictions and visa requirements.