Ireland has voted no in a referendum on the Lisbon Treaty. The document includes various rules designed to make the EU run more smoothly, now that it contains 27 nations. But the Irish no vote means it's likely it'll never come into force, at least not in its current form.
The EU's not just looking for a Plan B now, but a Plan C. The Lisbon Treaty is very similar to the EU Constitution, which was scrapped when French and Dutch voters rejected it in 2005. This time, 26 of the 27 EU countries, including Britain, decided they didn't want a referendum. Publicly, governments argued such a vote wasn't necessary because the treaty wouldn't dramatically change the way individual countries are run. But really, EU leaders didn't want to hold votes because they feared the treaty would be rejected. Because of its constitution, Ireland had to hold a vote, and it produced the result EU leaders dreaded.
It's difficult to see what the EU can do now. As the club grows, it's becoming increasingly tough to run, with even slower decision-making and more of the bureaucracy the EU is notorious for. Pressure's likely to be put on Ireland to hold another referendum on a slightly different version of the treaty. Similar things have happened in Ireland and elsewhere in the past, but forcing a further vote would be unpopular as it would show blatant contempt for the will of the Irish people. Plus, there'd be no guarantee the outcome would be any different.
Instead, look for the EU to have a third go at this in a couple of years time, when Croatia becomes the union's 28th member. Another new treaty would take a lot more slow, painstaking work to put together, and it would have to be less wide-ranging than either Lisbon or the original EU Constitution. But the EU's going to have to try. Otherwise it's going to become even less efficient, and therefore even more unpopular.