A will is a legal document that describes how you want your assets distributed at death. The actual distribution, however, is controlled by a legal process called probate, which is Latin for "prove the will." Upon your death, the will becomes a public document available for inspection by all comers. And, once your will enters the probate process, it's no longer controlled by your family, but by the court and probate attorneys.
Probate can be cumbersome, time-consuming, expensive, and an emotional trauma in a family's time of grief and vulnerability. Con artists and others with less than pure financial motives have been known to use their knowledge about the contents of a will to prey on survivors. A Living Trust avoids probate because your property is owned by the trust, so technically there's nothing for the probate courts to administer. Whomever you name as your "successor trustee" gains control of your assets and distributes them exactly according to your instructions.
There is one other crucial difference. A will doesn't take effect until you die, and is therefore no help to you with lifetime planning, an increasingly important consideration now that Americans are living longer. A Living Trust can help you preserve and increase your estate while you're alive, and offers protection should you become mentally disabled.