Ecumenism is, principally, dialogue between Christian groups aimed at promoting the restoration of unity among all Christians through understanding, through mutual respect and toleration, and through practical cooperation in areas of common concern, such as care for the poor, sick, and needy. In the Twentieth Century particularly, some ecumenical activities have drawn sharp criticism from various voices within the Orthodox Church, particularly participation in the World Council of Churches and, in the United States, the National Council of Churches of Christ in the USA.