Many estate tax plans use an "A-B" trust structure:

* The A trust may be called a marital trust. The assets in this trust are for the use of the surviving spouse. Bequests to a spouse, outright or in trust, avoid estate tax.

* The B trust may be called a bypass trust or a family trust. The assets in this trust can be left to the surviving spouse, to other family members, or to some combination of beneficiaries. The idea behind the B trust is that is will not qualify for estate tax exclusion as a bequest to a surviving spouse. Instead, the bequest to the B trust will be sheltered from tax by the federal estate tax exemption, now scheduled to be $1 million in 2011.

For example, suppose Kyle Dawson leaves $2 million to an A trust for his wife Lynn and $1 million to a B trust for his son Matt. No estate tax is due at Kyle’s death. The assets left in the A trust will be subject to estate tax at Lynn’s death but the assets in a properly drafted B trust will bypass estate tax indefinitely, no matter how large that trust grows in the future.