Estate taxes are different from and in addition to probate expenses, which can be avoided with a revocable living trust, and final income taxes, which must be paid on income you receive in the year you die.
Federal estate taxes are expensive (historically, 45%-55%) and they must be paid in cash, usually within nine months after you die. Because few estates have the cash, it has often been necessary to liquidate assets to pay these taxes. But, if you plan ahead, you can reduce and even eliminate estate taxes.