Under the U.S. Constitution as amended by the Sixteenth Amendment, any federal tax that is a quot;direct taxquot; (which is not an quot;income taxquot;) must be apportioned among the states in accordance with the respective populations of the various states. The purpose of this Article to solve the riddle of what is a quot;direct taxquot; that is subject to the apportionment requirement. Since the apportionment requirement can only apply inequitably across the nation, the correct labeling of any federal tax (other than an income tax) as a quot;direct taxquot; amounts to the proverbial quot;kiss of death,quot; as no such tax will be enacted. Recent commentary has staked out positions on this issue that I consider to be incorrect. Bruce Ackerman argues that that the Thirteenth Amendment (abolishing slavery) effectively repealed the apportionment-of-direct-tax clauses. Calvin Johnson argues that quot;direct taxquot; means only a tax capable (without effort) of being lt;igt;fairlylt;/igt; apportioned among the states in accordance with population, namely, a capitation tax or a tax on the states (a requisition). At the other end of the spectrum, Erik Jensen argues that quot;direct taxquot; means any personal tax other than an income tax. I argue, on the basis of constitutional text, the formation of the constitution, post-ratification history, function, historical evolution, and judicial doctrine that quot;direct taxquot; encompasses only (1) capitation (head) taxes, (2) requisitions, and (3) taxes on real estate. The apportionment requirement made quot;politicalquot; sense in the Framing period by linking the representation of states with the taxation of states, and also appeared to serve some narrow instrumental concerns. However, the theory is skewed, mainly because states are not really taxed as states, and states (as states) are only tenuously represented in Congress. Also, although apportionment dealt with some instrumental concerns, it aggravated others. I conclude that (apart from requisitions and head taxes), apportionment makes sense only with respect to real estate taxes, which is the nearest tax to a state tax. I also conclude that a real estate tax cannot be bootstrapped into validity as an quot;income tax.quot; Nevertheless, federal taxes on personal property and imputed income from real estate are constitutional, if endowment taxes are not.