Form 8379, the Injured Spouse declaration, is used to ensure that a spouseu2019s share of a refund from a joint tax return is not used by the IRS as an offset to pay a tax obligation of the other spouse.Before you file this, make sure that you know the difference between this and the Innocent Spouse declaration, Form 8857. You use Form 8379 when your spouse owes money for a legally enforeceable tax debt (such as a student loan which is in default) for which you are not jointly liable. You use Form 8857 when you want to be released from tax liability for an understatement of tax that resulted from actions taken by your spouse of which you had no knowledge, and had no reason to know.As the other answers have specified, you follow the Instructions for Form 8379 (11/2016) on the IRS Web site to actually fill it out.