So much of estate planning has focused on protection of the "non-taxable threshold" - otherwise known as a "credit shelter trust". In Massachusetts, that trust is usually limited to $1,000,000. In families where the first spouse passed away prior to the increase in the federal estate tax non-taxable threshold, that trust may be substantially larger. In any event, the credit shelter trust is designed to avoid estate tax in the surviving spouse's estate. With that avoidance,

"Portability" of a decedent's unused federal estate tax exemption refers to the election to add the exemption of a "first to die" spouse that is not needed to reduce federal estate tax to zero to the surviving spouse's federal exemption. Availing the surviving spouse of this benefit requires the predeceased spouse's executor to file a federal estate tax return, even if the only purpose is to make the portability election. In Matter of Estate of Vose, 2017 0K 3, Case Number: