Two errors of classification are defined: placing the low-risk offender in a high-risk category and classifying a high-risk offender in a low-risk category. The paper examines evidence suggesting that overclassification is widespread throughout the criminal justice system and that the rate of overclassification greatly exceeds that of underclassification. Endemic overclassification in people-processing bureaucracies is illustrated by medical and psychiatric diagnoses. Four general causes of systematic overclassification are analyzed: community attitudes and local politics, jail administrative policies and procedures, line staff motivations and practices, and problems in classification methods. For example, line staff are evaluated according to errors made in underclassification, and overclassification mistakes are seldom used as accountability standards. Moreover, methods used in jails are often primitive, highly subjective, and generate large numbers of errors in both directions. The paper identifies ways in which criminal justice classification must be improved and surveys three broad areas of intervention: improved methods, changes in jail administration policy and management; and reforms at the line level. Charts and 30 references.