If I am American citizen working in Korea (not a teacher) how do I pay my income tax?

Answer 1

You file a Form 1040, just like every other US taxpayer. If you have a tax debt, you enclose a check with your return.

As a US citizen living overseas you MIGHT be able to exclude part or all of your foreign earned income from US tax. You must file a timely return and meet certain tests to claim the exclusion. Alternatively you may claim a credit for foreign income taxes paid against your US income tax liability. You can choose whichever way results in the lowest US tax bill for you.

The rules on foreign earned income are complex and there are strict deadlines that must be met. See IRS Pub 54 for complete information, here's a link: http://www.irs.gov/pub/irs-pdf/p54.pdf