The Framers regarded bills of attainder and ex post facto laws as so offensive to liberty that they prohibited their use by both Congress (Article I, Section 9, Clause 3) and the states. The Framers had observed the use of bills of attainder by Parliament, particularly in cases of treason, and they were determined to deny the national legislature any such power. The Bill of Attainder Clause was part of the Framer’s plan to limit and refine what they saw as the unacceptable English abuse of the law of treason. As Justice Samuel Chase noted in Calder v. Bull (1798), the Framers applied the prohibition to the states “[t]o prevent such and similar acts of violence and injustice.” There is also historical evidence that the clause was designed to prohibit what the Framers observed as recent abusive state practices in the taking of private property.

The issue of ex post facto laws was more nuanced. Many of the Founders regarded retroactive laws, both civil and criminal, as contrary to the principle of legality itself. Roman law as well as Henry de Bracton (1210–1268), Sir Edward Coke (1552–1634), and Sir William Blackstone (1723–1780) in English law, and the influential Baron de Montesquieu (1689–1755), condemned the practice. Thomas Jefferson noted in an 1813 letter to Isaac McPherson, “The sentiment that ex post facto laws are against natural right, is so strong in the United States, that few, if any, of the state constitutions have failed to proscribe them.” At Philadelphia, some Framers, such as James Wilson, thought ex post facto laws so extra-legal that they were void ab initio; no textual prohibition was necessary. But a majority of the delegates wanted the prohibition stated in express terms.

All seemed to agree that ex post facto criminal laws were forbidden, but there was more ambiguity as to the validity of ex post facto civil laws. Part of the issue lay in the difference between a new law that changed preexisting legal obligations, and one that merely impacted (albeit severely) preexisting legal relationships. When Rhode Island, for example, issued a massive amount of paper money, it vitiated creditors’ holdings even though the legislature had not changed the terms of the contracts. Yet even here, some observers termed the issuance of paper money an ex post facto law. More seriously, other states did change the terms of contracts that is, of legal relationships, tolling the period for repayment. These kinds of measures constituted the “fluctuating policy” and “legislative interferences” that James Madison decried in The Federalist No. 44.

At the Constitutional Convention, George Mason moved to remove the ex post facto prohibition from the states precisely because he believed it would prevent some state retroactive legislation in civil areas that he thought beneficial. Elbridge Gerry supported Mason, but apparently only because he wanted the clause rewritten to apply specifically to civil cases. Mason’s motion was unanimously rejected. In the ratifying conventions, Anti-Federalists such as Patrick Henry also feared the impact of ex post facto prohibition on state economic legislation.

After the Convention, most Federalists believed the prohibition applied only to criminal statutes, a view adopted by the Supreme Court beginning with Calder v. Bull (1798). In Calder, Justice Samuel Chase noted that if the Ex Post Facto Clause (Article I, Section 9, Clause 3) applied to retroactive civil legislation, then the impairment of contracts clause (Article I, Section 10, Clause 1) would have been superfluous. As Robert Natelson has pointed out, in the end, the resulting prohibitions in the Constitution form a coherent pattern. The Ex Post Facto Clause prohibited retroactive criminal legislation, whereas the prohibition on the states from issuing paper money and from impairing the obligation of contracts covered the most objectionable forms of retroactive civil laws. Finally, the pattern was completed in the Fifth Amendment by the Takings Clause and the Due Process Clause, each of which limited the federal government’s ability to enact certain kinds of retroactive civil laws.

In recent cases, federal courts have applied the understanding of the Ex Post Facto Clause as applicable to criminal but not civil matters. So, for example, the Tenth Circuit found that a state regulation imposing a $25 monthly supervision fee on parolees did not violate the Ex Post Facto and Bill of Attainder Clauses because it was not punitive in nature and had legitimate legislative purpose. Taylor v. Sebelius (2006). The First Circuit held that a state constitutional amendment preventing the imprisoned from voting in state elections did not violate the Ex Post Facto Clause because there was a non-excessive and “obvious rational nonpunitive purpose for disenfranchisement.” Simmons v. Galvin (2009). In In re DNA Ex Post Facto Issues (2009), the Fourth Circuit found that requirements that prisoners must provide DNA samples and pay a $250 fee was not punitive enough to violate the Ex Post Facto Clause, but the requirement that the fee be paid before allowing a prisoner to be paroled or released did violate the Ex Post Facto Clause.

The substantive legal content of the Bill of Attainder and the Ex Post Facto Clauses in Sections 9 and 10 of Article I are fundamentally the same. Consult the entries on Article I, Section 9, Clause 3.