President Barack Obama has shrugged off criticism of the deal to limit Iran's nuclear development - saying it's good for American security.
The deal has been criticised by America's Middle East allies Israel and Saudi Arabia.
When you consider the diplomatic mountain the US and Iran have already scaled, you get a daunting sense of the challenge ahead.
The deal between Iran and world powers looks like a breakthrough, but with six months of wrangling over details ahead, it could still fail.
The nuclear agreement between Western powers and Iran was broadly welcomed by politicians, former world leaders and Middle East experts.