The potential for portability of a deceased spouse's unused exemption amount (DSUEA) to a surviving spouse was a significant change that emerged from the fiscal cliff legislation in 2010. However, early adoption of portability was limited, due both to a lack of awareness of the rule by many of those who needed it, and the fact that the portability rules were just "temporary" and faced future sunset until subsequently made permanent under the Taxpayer Relief Act of 2012... and by that time, it was already too late for many who might have wished to claim portability.
To provide relief for this unfortunate situation, the IRS has issued Revenue Procedure 2014-18, which will allow any decedent who passed away in 2011, 2012, or 2013 to have an extension to file an estate tax return and claim DSUEA portability for the surviving spouse. However, the relief provision reopening portability for anyone who died in the past 3 years is temporary; the Form 706 estate tax return must be filed by the end of 2014 to claim this "retroactive" portability, or the window will once again be closed for good.
For many surviving spouses, this opportunity for retroactive portability is an appealing relief provision to get a "free" second chance to claim portability and carry over a decedent's unused estate tax exemption amount; the only requirement is that a Form 706 estate tax return now be filed. In situations where the surviving spouse has also since passed away, the potential for retroactive portability could actually result in an immediate and significant estate tax refund. And notably, for same-sex spouses - who couldn't file for portability in 2011, 2012, or most of 2013 because the marriage wasn't recognized in the first place - the new relief provisions of Rev. Proc. 2014-18 offers the opportunity to go back and claim portability for a same-sex surviving spouse who never had the opportunity in the first place!