An A-B trust is a revocable living trust which divides into two trusts upon the death of the first spouse. This type of trust makes use of both the estate tax exemption ($3.5 million per person in 2009) and the marital deduction to make it so that no estate taxes are due upon the death of the first spouse. The B Trust is also known as the Bypass trust and it contains the amount of that years applicable exclusion amount. The A trust is the marital deduction trust which will typically contain both the surviving spouse's separate property and one half community property interests but also the residue of the deceased spouse's estate after the estate tax exemption has been utilized by the B trust. The use of an A-B trust ensures that both spouse's applicable exclusion amounts are effectively used, thereby doubling the amount of property which can pass to heirs free of Federal Estate Taxes.