Eighteen months of tough negotiations, twice extended, have yielded a framework agreement to cap Iran's nuclear program. Final details remain to be worked out by a June 30 deadline, but what is available is encouraging. If this deal succeeds, it will remove a source of great instability in the Middle East and could facilitate Iran's building of a new relationship with the rest of the world. Opponents remain unconvinced and skepticism is a good thing. Nevertheless, they have yet to articulate an alternative policy that makes sense. That remains the bottom line for any deal.

The agreement reached after eight days of talks in Lausanne, Switzerland, obliges Tehran to cut by two-thirds its supply of centrifuges, and keep only its earliest-generation centrifuges. Iran will enrich uranium to just 3.67 percent, a level far below that necessary to make a nuclear weapon, and will reduce its stockpile of enriched uranium by 97 percent. The core of the reactor at Arak, which could produce plutonium (another pathway to a bomb), will be dismantled and replaced and the spent fuel will be shipped out of the country.

Iran also promised to give the International Atomic Energy Agency access to all its nuclear facilities and to its nuclear supply chain. In return, the United States, the European Union and the United Nations will lift all nuclear-related sanctions once Iran is deemed to have honored its half of the deal. Other sanctions, such as those pertaining to terrorism, human rights abuses and non-nuclear weapons will remain.