The “evolving standards of decency” doctrine, which affords Eighth Amendment protection to punishment practices that violate contemporary standards, has historically played a key role in interpreting the nebulous Cruel and Unusual Punishments Clause, although the journey has been marked by controversy and contradictions. Today, as the continued vitality of the evolving standards doctrine has been increasingly called into question, it is worth pausing to remember where the doctrine came from, how and why it came about, and the work it has done and is poised to do going forward. This chapter touches upon each of those topics, first discussing the origins of the evolving standards doctrine and how it revitalized the Eighth Amendment, then turning to the power of the doctrine and the problems that developed as it came into full flower, and then finally turning to the doctrine’s potential going forward. The power, problems, and potential of the evolving standards doctrine are what make the doctrine a lightning rod of criticism as well as a beacon of hope for progressive decisions to come, rendering it one of the most interesting and important areas of Eighth Amendment law.