IRS Form 56 must be filled out by those who want to represent another taxpayer as a fiduciary. The difference between filing IRS Form 56 and a Power of Attorney is that when one is a fiduciary, one can make decisions as if they were the taxpayer whereas with a Power of Attorney, one can only carry out instructions issued by the taxpayer. Those who are taking over a decedent’s estate must fill out IRS Form 56, which allows them to manage the tax affairs of a deceased taxpayer, whether they are appointed by the court or by a will.