It's the largest disruption to air traffic since 2001 as the Icelandic volcanic ash continues to spew into the sky.
This weekend, three out of every four flights are canceled in northern and central Europe. Paris's Charles De Gaulle and London's Heathrow have been shut down.
If you're stuck in the U.S. because your flight is canceled, you're at the mercy of your airline. Fortunately, the airlines have been relatively accommodating in this crisis. American and Delta, for example, are allowing passengers to rebook their departure at any time up to the end of the month. Some airlines, such as British Airways, are also allowing passengers to re-route their itinerary at no charge in cases when a nearby airport may have earlier departures out to a destination.
Here's a clip from this evening's NBC Nightly News, featuring a quote from a Budget Travel editor.
Slide show from ForeignPolicy.com: How Iceland stopped the world in its tracks.