will first be determined by your and your spouse's resident or nonresident
status, each determined separately.
Both you and your spouse are subject to US income tax as nonresidents unless you have a green card or meet the substantial presence test and then you are taxed as a resident and have to report your worldwide income as subject to US income tax.
The substantial presence test is that you are present in the US for at least 31 days in the current year and at least 183 counting all of the days present in the current year, 1/3 of the days in the prior year and 1/6 of the day in the second prior year.
For more details see http://www.irs
As nonresidents, the only income subject to US income tax is:
1)Income that is Effectively Connected with a trade or business in the United States
2) U.S. source income that is Fixed, Determinable, Annual, or Periodical (FDAP)
For more details see http://www.irs.gov/Individuals/International-Taxpayers/Taxation
Salaries, wages or compensation
of nonresident aliens is based on where the services are performed, regardless of where paid.
For details see http://www.irs.gov/Individuals/International-Taxpayers/Source-of-Income---Personal
"All wages and any other compensation for services performed in the United States are considered to be from sources in the United States. The place where the personal services are performed determines the source of the personal service income, regardless of where the contract was made, the place of payment, or the residence of the payer."
If neither of you are residents due to substantial presence then you can file Form 1040
-NR jointly and report only US source income.
If you are a resident due to substantial presence you will have to use Form 1040 and report your worldwide income.
Generally, you cannot file as married filing jointly
if either spouse was a nonresident alien at any time during the tax year.
You can only file jointly if you and your spouse elect to have the nonresident spouse's worldwide income on that joint return
For more details see http://www.irs.gov/Individuals/International-Taxpayers/Nonresident-Alien---Figuring-Your-Tax
Please ask if you need more discussion or clarification.