Income Taxes in South Korea
Most Americans working in South Korea can expect to pay income taxes on their salaries to the Korean government. The tax year runs through December 31. Generally employers file the forms for their employees, but if not, individuals are required to submit their own. Here's a tax scale online.
Some Americans are exempt from paying Korean taxes according to the U.S.-Korea Tax Treaty. Those who qualify must reside in Korea for two years or less and must be there solely for research or teaching purposes at a university, research institution, or university-operated institute.
As an American working abroad, you will be exempt from U.S. income taxes as long as you make less than US$96,000 annually. You should still file a tax return with the Internal Revenue Service. Even though you may not owe any money, not filing can result in huge hassles years down the line when you have long forgotten your failure to file. The burden will be yours to prove to the IRS that you were actually overseas at the time and that you didn't make enough money to require any tax payment.
For complete information, the IRS publication "Tax Guide for U.S. Citizens Abroad," is available through the IRS and the various embassies.