Are you an American missionary living and working overseas? If so, you may be able eligible for the foreign earned income credit on your federal income tax. You may qualify to exclude up to $91,400 of your foreign earnings. You will need to satisfy either the bona fide resident test (a full tax year abroad) or the physical presence test (330 days abroad within 12 months) to qualify. See the flow chart below to learn more.
from IRS publication 54
If you rely on a family member of friend to file your federal income tax, you need to complete a form 2848. This form expresses to the IRS that you wish for the person named to sign your tax return and represent you in any communication with the IRS.