By Martin Asser
BBC News Website
The prisoner swap deal between Israel and Egypt is one of the most vivid signs of a warming in the "cold peace" between the two countries.
The detention of Israeli Druze businessman Azzam Azzam by Egypt had long been a point of contention between them.
Optimism in 1979 has failed to develop into close ties
His release comes days after Egypt's foreign minister and intelligence chief met the Israeli prime minister in Jerusalem.
Cairo is also reported to be considering sending an ambassador back to Tel Aviv after a long absence, and take on a security role in Gaza with Israel due to pull out next year.
After the establishment of the Jewish state in 1948, Israel spent 30 years at war with its giant neighbour and another 25 years in what both sides admit is a cold peace.
The wars and subsequent peace have always been determined by the Palestinian situation.
So after the outbreak of the Palestinian intifada (uprising) in September 2000, relations became positively icy.
Cairo backed away abruptly - withdrawing its ambassador and spearheading Arab opposition to Israel's policies in the occupied territories.
Israel meanwhile has been highly critical of the Egyptian government for allowing - as Israeli sees it - a vicious anti-Israeli attitude to prevail in the media.
What Egypt has never done is repudiate the 1979 Egypt-Israel peace treaty which was meant to define relations between the two countries.
These included the de-militarisation of the Sinai peninsula, normal diplomatic, economic and cultural relations, the free movement of goods and people and mutual protection under the law.
The treaty is also the basis of Egypt's strong ties with the United States and the billions of dollars of American aid it has received since it was signed.
There was a great sense of optimism back in the late 1970s and early 80s, when the then Egyptian and Israeli leaders won Nobel prizes for their role in agreeing the first peace treaty between Israel and an Arab state.
In November 1977, Egypt's President Anwar Sadat broke the long and bloody impasse by flying to Israel to deliver a message of peace directly to its leaders.
His offer was conditional on Israel's pulling out of all the territories it occupied in the 1967 war, including Egypt's Sinai peninsula.
A year later, days of talks at the US presidential retreat in Maryland resulted in the Camp David Accords, laying out Israel's commitment to withdraw from Sinai in exchange for normalising relations with Egypt.
They also included a formula for a two-state solution to the Israeli-Palestinian issue, giving Palestinians autonomy in the West Bank and Gaza.
The peace treaty was finally agreed and signed on 26 March 1979.
For Israel it was a major breakthrough, though it meant giving up all the strategic advantage gained by seizing Sinai in 1967.
For Egypt, it meant an end to a long and draining conflict, but it also brought hostility and years of being ostracised by Arab allies for allowing itself - the most potent Arab military power - to drop out of the Arab-Israeli conflict.
It also sealed Sadat's fate. He was assassinated by Egyptian Islamic militants during a military parade on 6 October 1981.
In many ways, the future of Egyptian-Israeli relations is secure - or as secure as anything in the Middle East in its current state.
Both sides have too much to lose from abandoning the status quo.
Some Israeli analysts wonder how Egypt will position itself towards Israel following the departure of its long-standing leader, Hosni Mubarak.
There is also the question of how the Israeli-Palestinian conflict will develop in the aftermath of Yasser Arafat's death, not to mention the US "war on terror", which has caused much anguish for Egypt and America's other allies in the region.