M.Jur. Hebrew University, Jerusalem, 1955; 
Ph.D. University of London (LSE), 1961; 
Dr. Jur. h.c. Yeshiva University, New York, 1981. 
Law Clerk to Justice E.D. Goitein of Israel Supreme Court, 1955-6. Assistant to Judge-Advocate-General, Israel Defence Forces, 1956-9. 
Admitted to Israel Bar, 1959. Assistant Legal Adviser, Israel Ministry for Foreign Affairs, 1962-5.
Joined Faculty of Law, Hebrew University, in 1965. 

  
Director, Harry Sacher Institute for Legislative Research and Comparative Law, Hebrew University, 1977-8. UNESCO Fellow, University of Sydney, Australia, July-August 1968, and UN Office of Legal Counsel, New York, September-December 1968. Senior Research Scholar, University of Michigan Law School, Ann Arbor, 1969. Visiting Professor at schools of law, University of Texas at Austin, 1971; New York University 1975-76; University of Michigan, Ann Arbor, 1985; Yeshiva University (Cardozo School of Law), February-March 1991; University of Southern California, Los Angeles, 1991-2; Tulane University, New Orleans, February 1994; University of Miami, January-February 1999. Member of Israel Delegation to 3rd UN Conference on the Law of the Sea, New York, 1973, and 31st session of UN General Assembly, New York 1976; Ambassador and Permanent Representative of Israel to the United Nations, New York, 1978-84. Member of Israeli negotiating team on peace treaty with Egypt (Camp David, February 1979; Blair House, March 1979). Member of Israeli legal team, Taba Arbitration (Israel-Egypt), 1986-8. Law Editor of the Encyclopedia Hebraica, 1973-8.

  

Main research interests: international organizations; international constitutional law; United Nations law. 

  
Publications include Historic Titles in International Law, 1965; Secure Boundaries and Middle East Peace, 1971; For Zion's Sake, 1987; Eroding the United Nations Charter, 1993; as well as over 40 articles in Hebrew, English and German, on various international law topics.