Armenia and Turkey are set to normalise their ties after a century of hostility stemming from the mass killings of Armenians under the Ottoman Empire. The BBC's Jonathan Head and Tom Esslemont analyse attitudes towards the deal in both countries.
JONATHAN HEAD IN ISTANBUL
Turkey, a fast-growing regional power running the world's 17th largest economy, would appear, on the surface, to need a deal far less than Armenia, a small, land-locked country still mired in post-Soviet poverty. Yet the current Turkish government has pushed just as hard to get it.
The governing AKP of Prime Minister Recep Tayyip Erdogan, which came to office in 2002, is focused far more on maintaining rapid economic growth and rising living standards among its mainly poor and lower middle-class voters than it is on old nationalist taboos.
To that end it has followed a foreign policy it calls "Zero Problems With Neighbours".
As well as backing the peace process with Cyprus and launching a bold initiative to end the conflict in the eastern Kurdish region, the AKP has sought to speed up accession to the European Union.
Mending ties with Armenia is one of the conditions laid down for EU membership.
When the Soviet Union broke up in 1991, Turkey was among the first countries to recognise Armenia as an independent state, but formal diplomatic relations were never established.
There were two serious obstacles that Turkey argued had to be overcome before diplomatic relations could be established.
One was to set aside any link to the Armenian campaign to have the mass killing of ethnic Armenians by Turkish troops in 1915 categorized as genocide, a term successive Turkish governments have refused to accept.
In that Turkey seems to have been successful. The protocol it is signing agrees that the "historical dimension" will be studied by a bilateral commission, to which international experts will contribute.
The other obstacle was over the disputed enclave of Nagorno-Karabakh in Azerbaijan, a state with close ethnic links to Turkey.
When, in 1993, ethnic Armenian forces took control of large swathes of territory around the enclave, the Turkish government closed the border with Armenia.
Mr Erdogan has promised the Azeri government that border will not be reopened until the conflict is resolved, and Armenian forces withdraw from Azeri territory they have been occupying outside the enclave.
In practice, Turkish negotiators have put the issue aside, viewing it as a parallel process which is being handled through mediation by the Organization for Security and Co-operation in Europe (OSCE). It is not mentioned as a condition for signing the protocol formally establishing diplomatic relations.
As in Armenia, the Turkish government will have to put the deal to parliament.
The nationalist opposition parties have said they will oppose it, but Mr Erdogan has a comfortable majority and will almost certainly get it through.
So long as discussion of the 1915 killings is kept low-key, most Turkish voters will probably support him.
He could, however, be held to his promise to Azerbaijan over Nagorno-Karabakh.
Progress is now visible over the enclave, following a three-hour meeting between the Armenian and Azeri presidents in Moldova - enough, perhaps, for Mr Erdogan to assuage his critics when he goes before parliament.
The protocol envisages full relations being established within two months of the signing ceremony in Zurich. All the signs are that this will happen.
TOM ESSLEMONT IN YEREVAN
The mass killing of hundreds of thousands of Armenians in 1915-18 is still a huge issue here. The fact that Turkey has not recognised them as a systematic "genocide" is very painful, especially for those who are descended from the victims of the deportations and executions.
Protesters say opposition to the deal could grow once it is signed
The protocol mentions no pre-conditions for Turkey to officially recognise genocide before ratifying it. That has struck a nerve with those in the wider Armenian diaspora and here in the homeland.
It has sparked protests in cities with big Armenian populations, including Beirut and Los Angeles.
At home, it led to one of the parliamentary parties - the "Dashnaks" - pulling out of the governing coalition in protest.
So, why does the Armenian government want to pursue rapprochement at all, given all the controversy?
The first reason is that the Armenian President Serge Sarkisian has come under mounting pressure from the European Union to make progress. He was strongly criticised by the West in 2008 after the authorities orchestrated a violent crackdown on pro-opposition demonstrators in Yerevan after a presidential election they say was rigged. Analysts say he now needs a foreign policy success to boost confidence in his leadership.
Secondly, there is great will on the part of the US and the EU to move things forward in terms of rapprochement.
Thirdly, Armenia cannot afford in the long term to keep its borders closed. Currently, trade with Turkey relies heavily on Georgia for transit. Its border with another neighbour, Azerbaijan, remains closed since the two went to war over the region of Nagorno Karabakh in the 1990s and Armenia would probably benefit economically from an open border with Turkey.
However, these reasons alone will not satisfy the opponents of rapprochement.
Importantly, Armenians feel they have not been consulted on opening the border with Turkey without Ankara's recognition of genocide.
An editorial in Armenia's Zhamanak newspaper in early September read: "The point is that the issue of the genocide is a national demand, which should not be made an axis of state policy."
As one anti-protocol demonstrator put it to me, even if the parliaments of both countries ratify the document - which could take time - opposition to the process of actually opening the border might even grow.