Nearly all EU countries have abolished passport controls. Anyone is free, for example, to travel from France to Slovakia or from Estonia to Sweden without the need for a passport. (That applies just as much to 'outsiders', such as Americans, Nigerians or Cambodians, as it does to EU citizens. There are no passport checks whatsoever within nearly all of the EU).
Only two countries have not fully signed up to the 'Schengen Agreement' (which creates a unified border-free European zone). One country has done so by choice. (Surprise, surprise - it's the UK!). The other is forced to stay out of the Schengen Zone by an existing agreement, even though it would like to join. (That country is Ireland. It can't become part of the Schengen Zone because of the open border between Northern Ireland and the Republic).