In this paper, simulation models of the California criminal justice system are created and validated with historical data in order to provide a plausible baseline upon which to base future projections. Different policy scenarios are simulated to the year 2030 to assess experimentally the likely consequences to prison populations and to evaluate how well these policies target the “dangerous offenders” proponents that these policies promise to remove from society via incarceration. It is noted that criminal sentencing reforms that have as their ostensible goal the protection of the public through the mechanism of selective incapacitation have proliferated in recent years, with the most prominent of these types of reforms being the “Three Strikes” laws. Because these changes to sentencing policy work by extending the term of incarceration for affected offenders, rather than by changing the rate of incarceration, many years must pass before the effects of these kinds of changes can be measured and evaluated by conventional statistical methods. The authors indicate that data-validated dynamic systems simulation modeling offers the opportunity to evaluate prospectively the effects of such changes on prison populations. In addition to providing descriptive and evaluative information about the likely consequences of these reforms to the compositional dynamics of prison populations, dynamic systems simulation modeling is also credited with affording the opportunity to experiment upon the system to examine prospectively the likely effects of policy changes. Validation data for this work was obtained from the California Criminal Justice Statistics Center and the California Department of Corrections. Figures, tables, references