FOR EU CITIZENS
The Schengen 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.
You will therefore need to present a valid passport or national identity card (ID) when travelling to the five non-Schengen countries and a valid passport when entering or leaving the EU at the external borders. Have your travel document always with you when travelling in the EU because they may be required for identification or security purpose. Be aware that the only valid ID is the one obtained from national authorities.
You will not need a visa for travelling within the EU.
FOR NON-EU CITIZENS
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 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.
For more information visit: www.mzv.cz