1. WHAT ARE THESE TALKS?
For a decade, Iran has been in dispute with the US and some European countries over its nuclear programme, which the "West" claims has a military component.
In 2009, discussions on a resolution resumed after a three-year break. The two sides --- Tehran and the 5+1 Powers (US, Britain, China, Russia, Germany, and France) --- made progress in the autumn, but the advance was halted by in-fighting within the Islamic Republic over the discussions.
Then, in spring 2010, another opportunity came and quickly went. Iran, working with Brazil and Turkey, offered to ship most of its 5% uranium out of the country for further enrichment. However, the US flatly rejected the Tehran Declaration.
Instead, Washington and European partners pursued an aggressive sanctions policy, first through the United Nations and then through their own measures. In the interim, Iran began moving towards production of 20% uranium, still at a level for civilian use but closer to development of the 90%+ uranium needed for a nuclear weapon.
High-level talks resumed in February 2012, but reached stalemate at Moscow in June. Sanctions have continued to escalate since then, while Iran has continued production of 20% uranium at the Fordoo plant, announced in 2009, and introduced new centrifuges at its Natanz plant, initially for quicker production of 5% uranium.
After months of manoeuvres, talks resumed in February 2013 in the Kazakh capital Almaty. Technical talks, lasting 13 1/2 hours, followed in mid-March in Turkey.
2. WHAT ARE THE ISSUES AT THE TALKS?
Until recently, the 5+1 Powers -- especially the US and the "European 3" of Britain, France, and Germany --- have pursued a "Stop, Ship, and Shut" approach. Iran will halt production of 20% uranium, ship existing stock out of the country, and shut the Fordoo plant.
In the February 2013 talks, the 5+1 Powers eased that position slightly, indicated that Fordoo could remain open, although 20% production would be suspended for at least six months with a view towards a permanent ban.
Iran does not want to commit to a permanent suspension, not least because it is concerned about a guaranteed supply of 20% uranium for civilian use such as medical isotopes but also because it sees the enrichment, carried out under the NPT, as its "inalienable right".
For this reason, the Islamic Republic wants recognition of its right to enrich.
In addition to this key concession, Tehran will also be looking for significant sanctions relief --- for example, removal of restrictions on the oil and financial sectors --- in exchange for any agreement to suspend 20% production.
So far the US and Europe have offered nothing more than a lifting of the ban on transfer of gold and precious metals to Tehran --- a measure which was only imposed on 6 February 2013 by Washington --- and a resumption of supply of parts for Iran's civilian aircraft.
3. WHAT IS THE WIDER CONTEXT
Although today's talks are specifically on the nuclear issue, both sides will enter the discussions with an eye on other events at home and abroad.
Iran is extremely concerned about its regional position, given the shaky status of its ally Bashar al-Assad in Syria and --- despite Tehran's rhetoric about the "Islamic Uprising", its name for the Arab Spring --- its failure to influence the region following the changes in the Arab world from 2011.
Conversely, the US and European partners insist that the Islamic Republic is threatening stability in the Middle East with its support of terrorist groups and subversion and its attempt to expand its presence and influence in neighbouring Iraq.
Both sides will also be looking back at domestic audiences and indeed playing to them. Iran's leadership is having to maintain an image of "strength" despite political and economic tensions --- many of them unconnected with sanctions --- and the US is always having to measure moves with an eye on a Congress which is likely to be hostile to any significant easing of sanctions without an Iranian capitulation.
4. WHAT ARE THE CHANCES OF SUCCESS?
Slim, at least in the sense of a major advance on the core issues.
As the talks open, both sides have played the game of urging the other to do the right thing and meet its agenda. While ostensibly more positive in tone than the US and Europe, Iran has said that discussion should be on the basis of its proposals, i.e., recognition of right to enrich and sanctions relief.
Meanwhile, American and European officials have said that Tehran must work with their proposals. These offer little in the way of easing of sanctions, beyond the token measures over gold, precious metals, and aircraft parts. They also appear to envisage a permanent halt to enrichment of 20% uranium, albeit in the immediate guise of a six-month suspension of operatoins at the Fordoo plant.
The March technical talks in Turkey did not offer the prospect of an agreement to finesse these different positions.
Unless Iran can get an iron-clad guarantee of long-term 20% supply and meaningful steps over sanctions --- and unless it is prepared to back down over its position that enrichment is a basic right of the Iranian people, a move that would be viewed poorly at home --- the best prospect at today's talks is for rhetoric about the chance for more discussions.
5. SO WHAT IS THE VALUE OF TODAY'S MEETING?
Simply that there are talks and likely to be more in the autumn, after June's Presidential elections in Iran. As long as both sides agree to continue, the option of an Israeli airstrike remains off the table.
That does not mean a resolution, of course. The US and the European 3 are likely to believe that the erosion of Iran's economic position will finally yield the concessions that they will not get this week. The Iranian regime will count on its public stance of a valiant defence of sovereignty rallying its people, despite the economic problems, and winning international sympathy.
But, for now, the avoidance of breakdown and the "worst" of military confrontation will do.