Delegates arrived early at the United Nations headquarters on Tuesday for international talks with Iran over its disputed nuclear programme.
The talks are resuming after a six-month gap.
Iran faces pressure to come up with ways to scale back its nuclear programme in exchange for relief from crippling sanctions.
But the talks in Geneva are seen as the best chance in years to end the deadlock in a decade-long dispute that could otherwise trigger a new Middle East war.
The election of relative moderate Hassan Rouhani as Iran's new president, and his pledges to smooth Tehran's international relations, have raised hopes of a negotiated solution.
Speaking on the eve of the talks the European Union's foreign policy chief said she was cautiously optimistic about the coming two days.
(SOUNDBITE) (English) EUROPEAN UNION FOREIGN POLICY CHIEF CATHERINE ASHTON SAYING:
"I hope that what we'll have here is a very productive two days, an opportunity to explor
