Each country has different requirements based on what passport you are holding (US or any other country). You may check with the consulate for each country you are visiting to get the most up to date visa requirements. It is your responsibility to ensure that you obtain the proper documents to travel.
If you are traveling to one of the 26 European countries and have a US or Canadian passport that is valid for at least 6 months beyond your travel dates, you will not require a visa at this time. You can get visa information and expedited services at ITSEASY.