In 1974, Massachusetts enacted a mandatory 1-year jail sentence for anyone convicted of carrying a gun. The 1973 New York law provided mandatory sentences for the sale and possession of illegal drugs. Both legislatures were attempting to reduce the discretion of prosecutors and judges in imposing sentences of incarceration on convicted felons. In both States, judges were unable to grant probation or suspend sentences for specified convictions. While no additional resources accompanied the Massachusetts law, the New York Legislature funded 49 new court parts (judges, prosecutors, defense counsel) to help carry the burden. Studies of the laws' implementation point out the profound differences between intentions and effect. Massachusetts police appeared to be more careful not to arrest innocent persons and increased their charging of 'possession' of a weapon as opposed to 'carrying,' the offense with the mandatory penalty. In New York courts, defendants redoubled their efforts to avoid or postpone sentencing, creating massive delays. In Massachusetts courts, judges were less likely to convict and defendants were more likely to flee before trial or appeal the outcome. Based on the two States' experiences, the report concludes that laws designed to eliminate sentencing discretion may displace that discretion in ways counter to legislative intent. To the extent that rigid controls can be imposed to avoid such displacement, the result may be to penalize some less serious offenders and postpone, reduce, or eliminate the punishment for more serious offenders. Finally, it is difficult, perhaps impossible, to substantiate the popular claim that mandatory sentencing is effective in reducing crime. Footnotes, graphs, 16 references, and the Massachusetts and New York laws are provided.