The effect of solitary confinement has been debated since at least the middle of the 19th century when both Americans and Europeans began to question the then-widespread use of solitary confinement of convicted offenders. A sizable and impressively sophisticated literature, now largely forgotten, accumulated for more than a half century and documented significant damage to prisoners. More recently the development of trial solitary confinement in Scandinavia revived interest in the topic and controversy over the findings. The weight of the modern evidence concurs with the findings of earlier research; whether and how isolation damages people dependents on duration and circumstances and is mediated by prisoners' individual characteristics, but for many prisoners, the adverse effects are substantial. (Published Abstract)