What aspects of human liberty does incarceration impinge? A remarkable group of Black and white prisoners, most of whom had little formal education and no resources, raised that question in the 1960s and 1970s. Incarcerated individuals asked judges for relief from corporal punishment; radical food deprivations; strip cells; solitary confinement in dark cells; prohibitions on bringing these claims to courts, on religious observance, and on receiving reading materials; and from transfers to long- term isolation and to higher security levels. Judges concluded that some facets of prison that were once ordinary features of incarceration, such as racial segregation, rampant violence, and filth, violated the Constitution. Today, even as implementation is erratic and at times abysmal, correctional departments no longer claim they have unfettered authority to do what they want inside prisons walls. And, even as the courts have continued to tolerate the punishment of solitary confinement in the last decade, a few lower courts have held unconstitutional the profound sensory deprivations such isolation has entailed. Prisoners have also sought procedural protections to constrain arbitrary decision-making about placements in solitary confinement and transfers to adverse settings. In response, the Supreme Court has required that, to state a Fourteenth Amendment claim that their liberty had been infringed, prisoners have to demonstrate that a specific practice imposed an “atypical” and “significant hardship.” What is typical in prisons? What are the sources of knowledge and the baselines used by Justices to decide? How did isolation come to be seen as an ordinary incident of prison life? We answer these questions through analyzing debates in both the U.S. Supreme Court and lower courts about what deprivations in prison are “normal.” After excavating the conflicts within the Court about the kinds of liberty interests prisoners retained, we mined hundreds of lower court opinions to learn how judges determine when constrictions on human movement meet the test of atypicality and hardship. By documenting the high tolerance many federal judges have for periods of isolation lasting months, years, and decades, we demonstrate the central role judges play in constructing the “normal” of prisons.