Peugh v. Davis is a United States Supreme Court case that addressed the issue of retroactivity of the United States Sentencing Guidelines. The case was brought by petitioner, Charles Peugh, who was convicted of bank fraud and sentenced to a prison term of 70 months. Peugh argued that the sentence he received was based on an outdated version of the Sentencing Guidelines, which had been amended after his conviction. He argued that the amended version of the Guidelines should have been applied to his case, and that the sentence he received was therefore unconstitutional. The Supreme Court agreed with Peugh, ruling that the Sentencing Guidelines must be applied retroactively. The Court held that the Guidelines must be applied to all cases that were pending on direct review at the time of the amendment, regardless of when the offense was committed. The Court reasoned that the Guidelines are not criminal laws, but rather are intended to provide guidance to judges in determining appropriate sentences. As such, the Court held that the Guidelines must be applied retroactively in order to ensure that all defendants receive the same treatment.

In the case of Peugh v. Davis, the Supreme Court was asked to determine whether a sentencing enhancement applied under the Federal Sentencing Guidelines should be considered in light of an amendment that had been passed after defendant's conviction but before his sentencing. The majority opinion held that this amendment did not apply retroactively and thus could not be used for consideration in determining defendant's sentence. However, Justice Breyer wrote a dissenting opinion arguing that it would be unfair to deny defendants like Peugh access to more lenient sentences when they were convicted prior to amendments being made which may have reduced their sentences if they had been sentenced afterwards. He argued that such an interpretation would violate due process rights by punishing those who committed crimes prior to changes being made and denying them access to potentially lower punishments available at later dates.