He attended the Hotchkiss School, where he was a member of the class of 1924 that included Roswell Gilpatric, Paul Nitze and Chapman Rose, before graduating from Princeton University in 1928.

Over the next year he traveled to Geneva, Berlin, the Soviet Union (with author Croswell Bowen), Poland, Rumania, Hungary, Yugoslavia, Spain, and Vienna.

Yost joined the U.S. Foreign Service in 1930 on the advice of former Secretary of State Robert Lansing, and served in Alexandria, Egypt as a consular officer, followed by an assignment in Poland.

After his marriage to Irena Rawicz-Oldakowska, he returned to the U.S. State Department in 1935, becoming assistant chief of the Division of Arms and Munitions Control in 1936.

He attended the Dumbarton Oaks Conference from August to October 1944, when he worked on Chapters VI and VII of the United Nations Charter.

He then served at the United Nations Conference on International Organization in San Francisco in April 1945 as aide to Secretary of State Edward Stettinius.

Yost set forth his views in a syndicated newspaper column, for The Christian Science Monitor, and in four books — The Age of Triumph and Frustration: Modern Dialogues, The Insecurity of Nations, The Conduct and Misconduct of Foreign Relations, and History and Memory.

In 1979, Yost was co-chairman of Americans for SALT II, a group that lobbied the Senate for passage of the second Strategic Arms Limitation Treaty.

[2] Yost's ancestors, who were driven out of the German Palatinate by Louis XIV's armies in the late 17th century, settled in the valley of the Mohawk River in New York State.