But the U.S. government is also a member of many  international organizations, and our representatives to these organizations, and the work they do, are called diplomatic missions, usually listed with a capital M, such as the U.S.  Mission to the United Nations. 

Missions are led by an  ambassador and do some of the same work as embassies but with an ear and an eye to  multilateral concerns: listening and reporting; communicating with media; advancing U.S. views; and negotiating with representatives of other countries and the staff from other  international organizations. 

The United States  Mission to the United Nations in New York City, for example, is the nation’s largest  mission to an international organization. It has a staff of over 200 people who represent the United States’ political, economic, legal, and military interests and American values at the United Nations.