Reno Leon Harnish III (born 1949)[1] is an American who was the director of the Center for Environment and National Security (CENS) at the Scripps Institution of Oceanography from 2009 to 2017.

He was a career member of the U.S. Foreign Service (American diplomat) and formerly served as principal deputy assistant secretary of state for Oceans, Environment and Science.

Before entering the Foreign Service, Mr. Harnish worked as a research assistant at the American Enterprise Institute, an international economist at the U.S. Department of Treasury, and as a clerk for Congressman Dave Martin of Nebraska.

Harnish served as the deputy chief of mission at the U.S. Embassy in Stockholm and engaged in Baltic Sea cooperation.

He completed his tour of duty in Baku in April 2006 immediately prior to taking his current position as principal deputy assistant secretary of state, Bureau of Oceans and International Environmental and Scientific Affairs.