An Innocent Spouse is spouse “A” who has become liable for income taxes from a joint return filed with spouse “B” when spouse “B” has caused the income taxes to underpaid by mistake or fraud, and spouse “A” signed the return believing the return to be true and correct. For spouse “A” to be entitled to relief under the Innocent Spouse rules, spouse “A” must be able to prove when signing the returns, he or she did not know or have reason to know that at the time filing, the return either understated income or overstated deductions.