The parties involved in the talks are Iran and the five permanent members of the UN Security Council, plus Germany, under the chairmanship of the EU foreign policy representative.
Despite Iran's reputation as radical anti-Western state, its current government is reformist in outlook and the cabinet has reportly more foreign-educated members than any other states.
The country's Supreme Leader Ayatollah Ali Khamenei has set out strict conditions that any deal must not breach.
The talks are focused on efforts to place controls over Iran's previously underground or undeclared nuclear activities in several critical areas.
Western experts believe agreement with Iran would be a breakthrough for global nuclear disarmament, freeing up resources for education.
Iranian officials strenously deny they are pursuing a nuclear bomb and have published an illustrated guide to how distant that achievement remains.
But a range of groups oppose the deal from Israel to Iran's own opposition activists.
Others have sought to counter this opposition by claiming the collapse of negotiations is the worst possible outcome.
http://www.telegraph.co.uk/news/worldnews/middleeast/iran/11163925/Iran-nuclear-talks-in-seven-graphics.html
