A: A Credit Shelter Trust, also known as a Bypass or A/B Trust is used to eliminate or reduce federal estate taxes and is typically used by a married couple whose estate exceeds the amount exempt from federal estate tax. Because of the Unlimited Marital Deduction, a married person may leave an unlimited amount of assets to his or her spouse, free of federal estate taxes and without using up any of his or her estate tax exemption. However, for individuals with substantial assets, the Unlimited Marital Deduction does not eliminate estate taxes, but simply works to delay them. This is because when the second spouse dies with an estate worth more than the exemption amount, his or her estate may be subject to estate tax on the amount exceeding the exemption. Meanwhile, the first spouse's estate tax credit was unused and, in effect, wasted. This could be avoided by ensuring that after the passing of the first spouse, an estate tax return is filed even if no taxes are due. The purpose of a Credit Shelter Trust is to ensure preservation of both spouses' exemptions. Upon the death of the first spouse, the Credit Shelter Trust establishes a separate, irrevocable trust with the deceased spouse's share of the trust's assets. The surviving spouse is the beneficiary of this trust, with the children as beneficiaries of the remaining interest. This irrevocable trust is funded to the extent of the first spouse's exemption. Thus, the amount in the irrevocable trust is not subject to estate taxes on the death of the first spouse, and the trust takes full advantage of the first spouse's estate tax credit. Special language in the trust provides limited control of the trust assets to the surviving spouse which prevents the assets in that trust from becoming subject to federal estate taxation, even if the value of the trust goes on to exceed the exemption amount by the time the surviving spouse dies.