This Article argues that, if the United States was going to have a workable, national income tax, the Sixteenth Amendment was legally and politically necessary in 1913, when it was ratified, and that the Amendment remains significant today. The Amendment provides that “taxes on incomes” need not be apportioned among the states on the basis of population, as would otherwise be required for direct taxes. An apportioned income tax would be an absurdity, and, without the Amendment, Congress could not enact an unapportioned tax on income from property, the sort of tax that was struck down by the Supreme Court in 1895 in Pollock v. Farmers’ Loan & Trust. The Pollock result was changed by the Sixteenth Amendment, but the core of the case has not been overturned. Indeed, in 2012, in National Federation of Independent Business v. Sebelius, Chief Justice Roberts favorably cited Pollock on a constitutional issue. All of that is to say that, without the Sixteenth Amendment, an unapportioned national tax on the income from property would continue to be invalid today. The Amendment is also important for what it does not say. It provides no protection for an unapportioned national tax on property if the tax is not treated as one “on incomes.” Such a tax on property would therefore be subject to the apportionment rule and, as a result, would make the tax difficult, and perhaps impossible, to implement.