One of the most frequent questions I receive from people is-Do I have to file a US tax return?
In general, US citizens and green card holders are required to file US tax returns reporting their worldwide income if their income exceeds a certain threshold. For example in tax year 2015 if you were single and under age 65 you would be required to file a return if your worldwide income exceeded $10,300. Attached are pages 8-10 from the IRS instructions to form 1040 which detail the various filing thresholds for tax year 2015. There are exceptions to this threshold- the most notable being if you have net self employment earnings (income less expenses) more than $400 you must file a US return. It best that you go over your personal situation with a tax professional to determine if you are required to file a return.