If you believe you're an injured spouse, you can file the federal Form 8379 for each year you're seeking relief. The form can be filed electronically or by mail, along with your tax return or on its own after you have filed your taxes.
If you mail a hard copy of Form 8379 with your 1040 tax return, you can write "Injured Spouse" on the top to make sure the IRS is aware before offsetting your refund. If you're filing the form separately from the return, make sure to list the Social Security numbers for yourself and your spouse in the same order they appear on your 1040 or related forms [source: IRS].
Form 8379 is relatively easy to complete. It begins with a series of yes/no questions to help determine whether the filer qualifies. It helps to have a copy of the joint tax return handy to itemize your income, adjustments, credits and payments. When you do file 8379, you should attach copies of W-2 or 1099 forms showing tax withholdings [source: TaxAct].
Individuals seeking innocent spouse relief file a completely different form: 8857 [source: IRS]. This form cannot be filed electronically. To file for innocent spouse relief, you must show you had no reason to know the understated tax existed or that you signed something you didn't understand [source: IRS].
Innocent spouse relief has recently been expanded to take into account abuse and controlling spouses. You can learn about special rules that apply in the IRS's "Publication 971: Innocent Spouse Relief."