With its population of 75 million, Iran would be the largest economy to rejoin the global system since post-Communist eastern Europe in the early 1990s.
"A young, educated population, a credit-based society with huge unsatisfied demand for everything from refineries and chemical plants to housing and basic infrastructure - the business opportunities are huge," said Emad Mostaque, a strategist who follows Iran at London-based NOAH Capital.
The size of the economic opportunities means political pressure to lift the sanctions could grow rapidly in Western capitals if nuclear talks seem to be going well.
But there would also be losers from an economic reopening of Iran. Some businessmen have prospered during its isolation - including some within Iran itself, who used political connections to profit from policies resisting the sanctions. They may lobby against the country's rehabilitation.