What does the Constitution mean when it says that “The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States” (U.S. Const. Article I, Section 8, Clause 1)? The definition of “tax” for constitutional purposes has become important considering the Supreme Court’s 2012 decision in National Federation of Independent Business v. Sebelius (“NFIB”), in which Chief Justice Roberts for the Court upheld the constitutionality of the individual mandate of the Patient Protection and Affordable Care Act (“ACA”) under the taxing power. This holding has resulted in commentators questioning the utility of Roberts’s distinction between a “tax,” where Congress’s power is nearly unlimited, and a “regulation,” where Congress’s power under the Commerce Clause is limited. We would propose a different distinction. A “tax” for purposes of the Taxing Clause is a pure tax: a tax implemented “to pay the Debts and provide for the common Defence and general Welfare of the United States.” Accordingly, a pure tax is intended primarily for raising revenue to finance the elected government’s policy and its implementation. Even a pure tax has constitutional limits; however, they are relatively few. The traditional bases for constitutional judicial review, such as discrimination based on gender, race, or sexual orientation, are applied to tax legislation in a very limited way. The Supreme Court has shown significant reluctance to review tax legislation in the U.S. on constitutional grounds. Nevertheless, one could argue that a tax provision that has a disparate impact on race, gender, or another protected category should be evaluated using strict scrutiny, as some provisions involving gender have been by lower courts. Other provisions should be reviewed on a rational basis ground, although we believe some of them should be struck down even on that basis. Pure taxes should be distinguished from regulatory taxes whose main purpose is not to raise revenue but are intended—in accordance with the rules of the free market—to impose the right economic price on those who financially benefit from the damages they cause to the whole community. Regulatory taxes include Pigouvian taxes, such as tobacco taxes and carbon taxes, which are designed to reduce negative externalities, and tax expenditures, which are negative Pigouvian taxes. They are designed to recognize the positive externalities that a particular behavior of a taxpayer that benefits the whole community. Therefore, all members of the community must compensate the taxpayer who created the positive externalities by paying the economic cost of the received benefit—through taxes higher than the taxes paid by the person who created the externalities. Regulatory tax legislation should be subject to constitutional review under various clauses of the Constitution, including the Due Process Clause, the Equal Protection Clause, the Establishment Clause, and the limits of the Commerce Clause. As discussed below, the “penalty” imposed by the individual mandate of the ACA, which was repealed in 2017, was a regulatory tax, not a pure tax, and therefore was subject to the limits on congressional power under the Commerce Clause, contrary to Chief Justice Roberts’s view. In our opinion, the individual mandate should have been upheld as consistent with these limits, per Justice Ginsburg’s dissenting opinion. [ABSTRACT FROM AUTHOR]