As this article from Forbes.com illustrates, if your spouse died in 2011, you will probably want to at least consider filing an estate tax return with the IRS to preserve your deceased spouse's portable estate tax exemption — even if the estate was well below the exemption level.  Due to the new portability rules, if one spouse dies leaving an unused exclusion amount, the other spouse may add it to his or her own personal exemption and effectively have up to a $10 million exemption.  However, to do so, the surviving spouse must file an estate tax return for the decedent.  No estate tax return, no portability.  You have up to nine months from the date of death to get the return on file, so the first returns for 2011 deaths are going to be due in just a few days.