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: Antra Viluma
Age: 34
Occupation: Marketing specialist
Country: Latvia, the new EU's poorest state
My main fear is that prices will go up when we join the EU and that salaries will not grow as fast. But I think there will be more gains than losses.
I voted for joining the EU at the referendum last year because I think the EU will bring more choices. It will be even easier to travel. I might to try my luck at finding a job abroad for a fixed period of time just to have the experience of working in another country. This won't happen tomorrow as I have two small kids and I would not want to leave them behind. A move would involve a lot of preparation but I might consider it in five to ten years time.
I hope that my children will have more opportunities too. I would like them to go and study abroad for a while - maybe for a postgraduate degree. I haven't had that experience myself but would be happy if they did.
Is there much left over from your salary at the end of the month and what do you use this money for?
I can't say that we have much left over from my salary at the end of the month. I don't really make any savings, but we have enough to go to the zoo, cinemas, coffee shops and theatre. This doesn't happen that often - we go to cinema perhaps once a month. Cinemas are getting more expensive. - a trip to the new multiplex could set us back by as much as 15 Lats (23 euros). One other treat is going to a restaurant - this also happens around once a month. This time we went to the Chinese and spent about 10 Lats there.
I don't spend much on children's clothes. We normally hunt for bargains and do most of our shopping during sales. We also get some clothes from older cousins.
What do you like about living in Latvia?
Well, Latvia is home. There is a positive feeling of a new beginning, but there is a lot waiting ahead. The nature is beautiful. There are many opportunities around for my children and me.
And what are the bad sides of living here?
Basically it's the feeling that I can't get all the things required for a normal life here despite my two good degrees and skills. For instance, I can't buy an apartment. Also, neither our health nor property is insured - we've been lucky so far and insurance premiums are one of the things we have to save on.
My employer, for instance, does not provide medical insurance for me and my family.
There is no safety cushion here - I received unemployment benefits on two occasions in the past but it's impossible to live off this money.
I'm lucky in the sense that I can choose jobs quite freely in my age. My older friends say it is hard to find a job after you are 50. This is part of the reason I am trying to accumulate as much experience and skills as I can for the future.