Answer: In most cases, it will depend on your purpose of travel and how long you plan to stay. Going to France for a week just to see the sights? You should be fine with just your U.S. passport. Going to Italy for a 6-month culinary arts internship? You’ll need a visa for that. Even within Europe, where nearly 30 countries are party to the Schengen Agreement and allow U.S. travelers to cross their borders without a visa, each country may have slightly different regulations or processing requirements. And before you start assuming that all European countries are the same, get this: Liechtenstein is not a Schengen member. Go figure. The rest of the world is similar to Europe, with each government establishing and enforcing their own requirements for international visitors. In some cases you must apply for a visa in advance, in other cases you get a visa when you arrive at the destination country, in other cases you don’t need a visa at all if your passport is valid for a certain length of time beyond your international travel.
To help sort out the requirements for international travel, the U.S. Department of State has developed a great tool which takes all the guesswork out of the visa requirements for U.S. citizens. Choose the country you plan to visit, and scroll down to the “entry/exit requirements for U.S. citizens” section for clear, accurate information about exactly what you’ll need to enter the country. This is available for every country from Afghanistan (visa required) to Zimbabwe (visa AND return ticket required!) and is updated when the regulations change.
While the U.S. State Department has collected and posted these regulations, it is important to note that the U.S. Embassy in Seoul does not have a role in assisting U.S. citizens with getting visas to other countries. The embassy or consulate of the country you wish to visit is your best resource for visa application information.