Studies of national sentencing statistics, court case files, and simulated judicial and prosecutorial decisionmaking reveal sentencing disparity unexplained by legal factors (i.e., offense and offender characteristics). A review of empirical research pertinent to the psychological and sociological backgrounds of disparity focuses on the factors that influence prosecutorial and judicial decisionmaking. Findings indicate that decisionmakers across and within jurisdictions have distinctive decisionmaking patterns based on individualized mental schema, responses to environmental stimuli, and task conceptions. Even though the decisionmaking structure may be similar for the decisionmakers, the way similar information is processed and perceived will produce differing decisions. Once decisionmaking patterns have assumed a distinctive character, the individual decisionmaker repeats them in the interest of consistency and familiarity, thus making it difficult to eliminate disparity among decisionmakers. 52 references.