Today almost all estate plans are accomplished though creation of a Trust or series of Trusts. There are good reasons for this. When your assets are transferred prior to your death to you as a trustee, and you name a successor trustee who will be in charge after your death or incapacity, no probate of your estate is required. This means that the administration is accomplished without court oversight, with greater privacy, within a shorter period of time, and with considerably less expense.
Without a Trust, your assets are administered through the probate process. The expense of a probate is significantly higher than the expense of a Trust administration. For example, if the gross estate value is $1 million, your probate fees would be $23,000 paid to the lawyer, and $23,000 for the personal administrator. Also, the probate process makes it easier for someone to challenge the estate plan.
The function of a Trust has changed dramatically in the last ten to fifteen years since the federal government revised the estate tax laws. There is no estate tax until the gross value of the estate is $5 million for an individual and, using an A-B Trust, $10 million for a married couple. An A-B Trust insures that upon death of the first spouse, a separate irrevocable Trust is funded and there will be no estate tax for the married couple's estate up to a gross value of $5 million. The federal "marital exemption" amount is subject to change.
Often Trusts have sub-trusts to address specific issues. For example, if a beneficiary is receiving public benefits, you would likely want to create a Special Needs Trust so that the intended beneficiary does not lose any benefits when they receive a gift from you. Or you may have a child who does not manage money well, and you want some oversight prior to distribution. You may have a married child and you want to insure that only your child and not the spouse receives your gift, or you may wish to designate funds specifically for a grandchild's education.
Finally, if you have a blended family with children from different marriages, you may want to make sure that assets of the deceased spouse are distributed to the child or children of that spouse after the death of the survivor spouse. That can be done with the creation of an irrevocable Trust.