The authors examine a model which specifies the relationships among criminality and the use of alcohol and other drugs. A pattern is hypothesized: The initiation of alcohol/drug use tends to progress from legal to illicit drugs; the early initiation of drugs increases the current use of drugs; and criminality is affected by the initiation/use patterns. Analyses based on data collected from individuals in jails, drinking driver programs, alcoholism treatment centers, and on probation indicate that the early onset of legal drug use induces the onset of illicit drug use. Criminality is affected by the current use of alcohol and cocaine. Comparison and contrast of findings from the four groups are provided.