When spouses file a joint tax return, each spouse is responsible for the entire tax liability. This is referred to as joint and several liability. Joint and several liability survives the divorce of the spouses even if the corresponding divorce decree states that one (1) of the spouses is solely responsible for any particular tax liability.
Innocent Spouse Relief is applicable to issues of understated tax in regard to joint and several liability. Innocent Spouse Relief is available, to the requesting spouse, when the other spouse or former spouse is shown to have improperly reported items or omitted items on their joint tax return. Innocent spouse relief can relieve the requesting spouse of joint and several liability for the tax, interest, and penalties that qualifies for such relief. Joint and several liability remains for the tax, interest, and penalties that do not not qualify for such relief.
To qualify for Innocent Spouse Relief, you must meet all of the following conditions: (i) you must have filed a joint tax return; (ii) there must be an understated tax, on the joint tax return, that is due to an erroneous item(s) of your spouse or former spouse; (iii) you can show that when you signed the joint tax return, you did not know and had no reason to know that the understated tax existed; and (iv) taking into account all the facts and circumstances, it would be unfair to hold you liable for the understated tax.
Internal Revenue Service Publication 971