The first flight out of O'Hare since last week departed Monday evening.
Seven million passengers have been affected and the airlines have lost more than $1 billion. The decision to begin flying again came after several European carriers performed tests flights in the volcano zone and reported no problems.
At O'Hare, flights began to take off and arrive from Europe Monday night.
Jacky Sheehan was hoping to leave for London. She has spent the last four days sleeping on cots and her money is running out. If she didn't get out Monday night she was told she won't get a flight for another 10 days.
"We've all got jobs to go to, children back home. We don't know what's going on. It's a bit tedious and frustrating," said Sheehan.
Two women arrived on the first flight to Chicago from Rome Monday afternoon.
"We knew as of late last night that we were good to go. We had a big going away dinner so we were informed at that time that we were good to go," said Sarah Smith.
Tuesday morning Europe will be divided into three zones: open skies, a so-called caution zone where some flights will be permitted and a much smaller no-fly zone than we've seen in recent days.
"We're going to have to trust to a certain extent but this is still something that's evolving almost on an hour by hour basis," said John Nance, ABC News aviation expert.
In Dubai, an Australian couple couldn't make it to the church on time in London, so the hotel lobby was transformed into a reception all. They used a video link for the minister to officiate as the duo was serenaded with "Here Comes the Bride."
"It was just the most amazing and with all the other stranded passengers around us singing and clapping and cheering it was more than we could ever have hoped for," said Natalie Mead, stranded bride.
The volcano could still alter plans because British authorities reported eruptions are strengthening and a new cloud is head for Britain. There are no international standards to mandate how much ash in the air makes it too dangerous to fly. Each airline makes its own call on whether to fly.