As time hurtles forward, new science constantly emerges, and many scientific fields can shed light on whether a punishment is unconstitutionally cruel and unusual, or even on whether bail or fines are unconstitutionally excessive under the Eighth Amendment. In fact, in recent years, science has played an increasingly important role in the Court’s Eighth Amendment jurisprudence. From the development of an offender’s brain, to the composition of lethal injection drugs, even to measurements of pain, knowledge of various scientific fields is becoming central to understanding whether a punishment is unconstitutionally cruel and unusual. There are a number of limits to how the Court can weave science into its decisions, though. For example, relevant data are difficult to come by, as ethical limitations prevent a wide swath of focused research that could be useful in this arena. Further, the Justices’ understandings of the complicated science that can help inform their Eighth Amendment decisions are limited. This chapter examines the relevance and limitations of science — both physical and social — in Eighth Amendment analyses.