With equal parts tedious paperwork and luck, you can stay in most countries for as long as you like. You'll find, however, that most countries offer U.S. citizens a reasonably long stay -- at least as long as a moderate vacation or business trip -- without all that messy paperwork. Visa regulations vary widely by country, so you'll have to research your destination before you go to know how long you can stay. And don't worry about staying too long and losing your U.S. citizenship -- U.S. citizens can return at any time, regardless of how long they've been abroad.

For Work

If you're traveling abroad to work, you'll need to obtain a work visa from your destination country. Getting work visas can be challenging, especially in countries with struggling job markets; they would rather give jobs to their citizens. Although, if you're highly qualified and can provide a needed service, your chances are much higher. Once you get your work visa, most countries allow you to stay for the duration of the work. The best way to approach getting a work visa is to contact the embassy and U.S. consulate of your destination country, as these departments usually have specific instructions for you to follow.

For Pleasure

Traveling for pleasure can be a little tricky, depending on where you go. You can visit the U.K. for as long as six months with just a valid U.S. passport, but China almost always requires a visa to enter -- and, even then, you're stuck with a small number of entries into the country. Like applying for a work visa, it's always best to contact the consulate of your destination country to find out any special requirements for entering and how long you can stay. For example, Argentina requires U.S. citizens to pay fees to enter the country. Most countries will allow you to stay for three months with the proper documents, but most also have exceptions to their rules.

For School

Studying abroad changes a lot of the rules for how long you can stay in another country. You're going to need a student visa and a school or program acceptance. In general, countries are more lenient with doling out student visas because of student exchange agreements and the fact that many study abroad students decide to stay abroad and apply their newly acquired skills to the job markets in their countries of study. Rules vary by country, but most allow students to stay for the duration of their studies on a student visa, with some requiring periodic renewals -- usually every five or six months.

For Good

Although it is extremely difficult in most cases, retiring or moving permanently abroad is possible. If you're planning on becoming an expatriate, you'll likely have to try several avenues before you completely work out your residence status. You won't have any luck getting a retirement visa to most of Europe or Canada -- they don't allow these anymore. The countries that do allow them have made them difficult to obtain in many cases. A 2012 "Forbes" article cites Thailand's policy of requiring retired expats to report to immigration authorities every 90 days as an example of the difficulties associated with retirement visas. If you're not quite to retirement and simply want to move abroad, you'll have to jump through your destination country's hoops for applying for a green card or permanent residence. Some countries, such as Italy, allow you to establish residency by renewing an extended visa every two years without working. After six years, you've established residency, as long as you can show that you were able to live there without working. Requirements will vary by country and depend heavily on the country's current needs and immigration laws.