There are no longer any frontier controls at the borders between 22 EU countries. This is thanks to the Schengen rules which are part of EU law. These rules remove all internal border controls but put in place effective controls at the external borders of the EU and introduce a common visa policy. All EU countries are full Schengen members except for Bulgaria, Cyprus, Ireland, Romania and the United Kingdom. Iceland, Liechtenstein, Norway and Switzerland are also Schengen members but are not in the EU.
You will therefore need to present a valid passport or ID card when travelling to the five non-Schengen countries and when entering or leaving the EU at the external borders. Carry them when travelling in the EU because they may be required for identification or security purposes. Be aware that the only valid ID is the one obtained from national authorities.
Make sure that any children travelling with you either have their own passport or ID card or are registered on your passport. However, from 26 June 2012, children will need to have their own passport or ID card to travel (even if they are still mentioned in their parent’s passport, which remains valid).
You will not need a visa for travelling within the EU.
You will need a valid passport.
There are 42 countries whose nationals do not need a visa to visit the EU for three months or less. These include Australia, Canada, Croatia, Japan, New Zealand and the United States. The list of countries whose nationals require visas to travel to the United Kingdom or Ireland differs slightly from other EU countries. Apply for a visa from the consulate or embassy of the country you are visiting.
If your visa is from a country fully applying the Schengen rules, it automatically allows you to travel to the other Schengen countries as well. Moreover, if you have a valid residence permit from one of those Schengen countries, it is equivalent to a visa. You may need a national visa to visit non-Schengen countries.
Border officials in EU countries may ask for other supporting documents such as an invitation letter, proof of lodging, return or round-trip ticket. For the precise requirements contact the local consular services of the EU country in question.