The US once saw the Soviet Union as its biggest nuclear threat, today, however, it is more concerned about what it calls "nuclear terrorism" - the risk of weapons falling into the hands of small groups or rogue states.
On Monday, more than 40 nations gather in Washington to attend the Nuclear Security Summit - the biggest gathering outside the UN on US soil since the 1945 San Francisco summit on forming the United Nations.
Barack Obama, the US president, first proposed the summit exactly a year ago in his speech in Prague, where he outlined his vision of a world free of nuclear weapons and nuclear threats.
But Iran has not been invited and Binyamin Netanyahu, the Israeli prime minister, has decided not to attend.
So where is the real threat today? Is the world nuclear order fair and does it work?
Inside Story discusses with guests: Bruno Pellaud, a former deputy director of the International Atomic Energy Agency (IAEA); Ezzi-dine Choukri, a professor of international relations at the American University of Cairo (AUC); and Avraham Diskin, a political scientist from the Hebrew University of Jerusalem.
This episode of Inside Story aired from Sunday, April 12, 2010.