As Sitges indicates, virtually the whole of the European Economic Area (which comprises the whole of the EU plus Switzerland, Norway and Iceland) is now a passport-free area, under the Schengen Agreement. No passport is required to move from any full Schengen member state to any other.
The UK is the only EU country which refuses to sign up to the full provisions of the Schengen Agreement but, for movements almost everywhere else in Europe, passports are totally unnecessary. Going from Paris to Berlin is just like going from London to Edinburgh. (i.e. you'll be travelling from one country to another but you'll be laughed at if you ask the locals where you should show your passport!).
See my post here for further information about the Schengen Agreement:
http://www.theanswerbank.co.uk/Travel/Question 744948.html
Chris