Marriage as defined by the federal tax code
http://www.irs.gov/publications/p17/ch02.html
Marital Status
In general, your filing status depends on whether you are considered unmarried or married. For federal tax purposes, a marriage means only a legal union between a man and a woman as husband and wife.
Unmarried persons. You are considered unmarried for the whole year if, on the last day of your tax year, you are unmarried or legally separated from your spouse under a divorce or separate maintenance decree. State law governs whether you are married or legally separated under a divorce or separate maintenance decree.
Considered married. You are considered married for the whole year if on the last day of your tax year you and your spouse meet any one of the following tests.
1. You are married and living together as husband and wife.
2. You are living together in a common law marriage that is recognized in the state where you now live or in the state where the common law marriage began.
3. You are married and living apart, but not legally separated under a decree of divorce or separate maintenance.
4. You are separated under an interlocutory (not final) decree of divorce. For purposes of filing a joint return, you are not considered divorced.
http://www.irs.gov/publications/p17/ch02.html
Marital Status
In general, your filing status depends on whether you are considered unmarried or married. For federal tax purposes, a marriage means only a legal union between a man and a woman as husband and wife.
Unmarried persons. You are considered unmarried for the whole year if, on the last day of your tax year, you are unmarried or legally separated from your spouse under a divorce or separate maintenance decree. State law governs whether you are married or legally separated under a divorce or separate maintenance decree.
Considered married. You are considered married for the whole year if on the last day of your tax year you and your spouse meet any one of the following tests.
1. You are married and living together as husband and wife.
2. You are living together in a common law marriage that is recognized in the state where you now live or in the state where the common law marriage began.
3. You are married and living apart, but not legally separated under a decree of divorce or separate maintenance.
4. You are separated under an interlocutory (not final) decree of divorce. For purposes of filing a joint return, you are not considered divorced.
