Kai Aage Eide (born 28 February 1949 in Sarpsborg) is a Norwegian diplomat. He was appointed the United Nations Special Representative to Afghanistan and Head of the United Nations Assistance Mission in Afghanistan (UNAMA) on 7 March 2008.

Eide previously served as the Special Envoy of the United Nations Secretary-General in Kosovo in 2005 and as Special Representative of the Secretary-General in Bosnia and Herzegovina in 1997-1998.

He has been a member of the Norwegian Foreign Service since 1975. He was the Norwegian ambassador to North Atlantic Treaty Organization (NATO) from 2002 to 2006 and to the Organization for Security and Cooperation in Europe (OSCE) from 1998 to 2002. He has also been posted as Special Adviser on the Balkans at the Norwegian Ministry of Foreign Affairs and as Norway's ambassador at the International Conference for the former Yugoslavia.