Computer simulation provides a means of answering that 'what if' questions without having to submit to trial and error in real-world applications of new policy. A computer simulation can provide decisionmakers with realistic information at minimal cost in a relatively short time without having to deal with the political and legal restraints of the real world. The use of the simulation model can be illustrated in a hypothetical experiment to determine the effects of decriminalizing marijuana use. The simulation showed that about one-fifth of the cases currently being processed in felony criminal courts are prosecutions for possession of relatively small quantitities of marijuana. Processing time for marijuana cases is roughly the same as for all other felonies. The decriminalization of marijuana would thus have a significant impact on the courts in freeing them to speedily process other forms of criminal cases. Whether or not recommendations from a simulation are used, however, depends upon political decisionmaking; e.g., even though the decriminalization of marijuana would significantly reduce court caseloads, many legislators might feel that the use of marijuana is a sufficiently odious and dangerous practice to be outlawed. Still, simulations do provide information relevant to decisionmaking regardless of the political influences that may ultimately determine how the simulation results are handled.