Tony Blair, pleading the state opening of Parliament, his recent attendance of the Commonwealth summit in Durban, and the finely poised Irish peace process, will be one absentee. Another is Lennart Meri, Estonia's President, who is staying away in protest at events in Chechnya. Nor will Franjo Tudjman, Croatia's dying President, be there.
But almost everyone else will be: Bill Clinton, Boris Yeltsin and an army of Presidents and Prime Ministers from the OSCE's 54 members, made up of the countries of the Nato alliance and the former Warsaw pact, the successor states to the Soviet Union, and the rest of Europe's non-aligned and neutrals, great and small.
How do so many people gathered around a single table, actually hold discussions ? The answer is, they don't. The nine hours of formal sessions tomorrow and Friday will be taken up by formal statements (that of Robin Cook, leading the British delegation in the absence of Mr Blair, is number 16 on the list). The real business gets done on the sidelines, in bilateral meetings and caucuses. And this time there is plenty of it.
The summit will be one of the last foreign sorties of Mr Yeltsin, plagued by ill-health and due to step down next summer. And the Russian President will have to defend his country's ever more indiscriminate onslaught against Chechnya, the issue which overshadows the gathering.
Mr Yeltsin prides himself on his warm personal ties with his colleagues, not least President Clinton. But this time a jovial "Bill and Boris" show is not on the cards. The OSCE, linear descendant of the 1975 Helsinki accords, is said to be Russia's favourite international organisation, the European body it would like to take precedence over Nato. But on Chechnya, the Russian leader is virtually isolated. And if proceedings in Istanbul go completely off the rails, two important documents - an amended treaty limiting conventional forces in Europe and a new European Security Charter - may not be signed as planned. That would merely underline the increasingly obvious, that relations between Russia and the West are worse than at any time since the end of the Cold War.
Nor are other important issues likely to go Russia's way. Azerbaijan, Georgia and Turkey are due to sign agreements for an oil pipeline from Baku to the Turkish Mediterranean coast which, if built, would weaken Moscow's hand in the new Great Game over Caspian and Central Asian oil.
Armenia and Azerbaijan should make further progress towards settling their dispute over the enclave of Nagorno-Karabakh. If a peace deal is reached, Russia's scope for mischief-making in its old fiefdom of the southern Caucasus will be significantly reduced.
And Nato's most implacable rivals, Greece and Turkey, plan informal talks on Cyprus that may help next month's meeting in New York between leaders of the divided island's Greek and Turkish communities, the first in two years.Reuse content