When a married couple files a joint tax return, they are “jointly and severally” liable for the tax payments. What this means, practically speaking, is that the IRS can come after either spouse or both of them for a tax omission or underpayment, even if only one spouse was the real culprit. This includes back taxes, penalties and interest. In fact, one spouse may be held liable even if he or she was completely unaware of the situation. And getting a divorce afterward doesn’t get you off the hook.