The new EU will stretch more than 3,000 kilometres from east to west, spanning three time zones and a dramatic array of climates.
The smallest EU state will be home to just a few hundred thousand, the largest will boast nearly 90 million. The average yearly income in one country will not be much more than the typical monthly wage in another.
In a Europe of such contrasts, BBC News Online asked those living in the extremities to discuss their hopes and fears for the future of an enlarged EU.
Name: Rose Grech
Age: 29
Occupation: Computing teacher
Country: Malta, the new EU's most devout state
The first time we were asked whether we wanted to join the EU or not I think I was 11-years-old. Somehow, at that age, I already knew deep inside that I wanted to be part of the EU. I always thought it would be like being part of a big family where everybody helps each other.
Today, Malta needs help from other countries for some of its problems, like pollution, traffic, and the very bad environmental problems we have. Nobody in this country really takes care of it, but now they have to, because there are certain EU standards that we have to meet.
Now Malta will become part of a very, very big group of counties and we have a voice in this union. If, God forbid, we had said no at the referendum, Malta would be completely isolated now. We are very energetic people, but we are so small that we can't stay on our own. We have to be part of the EU.
Overall I am very optimistic. My main concern is about the attitude the Maltese will have towards joining. The first few years will be very hard until we adjust, I think. We are very bad at adjusting to changes. But in the long run, everything will be OK.
What role does the Church play in Malta's everyday life?
I think it's got to do with our upbringing. This is a very small community, just like a big family - especially Gozo, the island where I live. We have been Christian for many, many generations.
The average Maltese goes to mass regularly. Many people go every day, although among younger people, the majority go only on Sundays. I think that every village in Gozo has got a church and a local "festa", a traditional festival for the patron saint with processions, and absolutely everybody takes part in it.
Do you think that EU membership will have an impact on this religiosity in Malta?
I don't think so. We are very strong. Our leaders, and especially [President] Eddie Fenech Adami, were adamant that membership would not change our values, which have been with us forever. For example, abortion: I think, and I hope, that it will remain illegal. Politicians have been very clear about this, because people were afraid that we would become like other countries where everything is allowed.