Police decisions not to invoke the criminal process largely determine the outer limit of law enforcement. By such decisions, police officers define the ambit of discretion throughout the criminal process of such other decision-makers as prosecutors, grand and petit jury judges, probation officers, correctional authorities, and parole and pardon boards. Police decisions not to invoke the criminal process are generally of extremely low visibility and are seldom the subject of review. Yet, an opportunity for review and appraisal of non-enforcement decisions is essential to the functioning of law in the criminal justice system. The author attempts to determine how the visibility of police decisions not to invoke the criminal process may be increased and what procedures should be established to evaluate these decisions on a continuing basis in light of the complex objectives of criminal law. He notes that criminal law is one of many interrelated mechanisms for the social control of human behavior and that police officers have a duty not to enforce criminal law unless invocation of the criminal process can be achieved within certain bounds. The author cites as examples trading enforcement against a narcotics suspect for information about another narcotics offense or offender and the police decision not to invoke a felonious assault law unless the victim signs a complaint. The author concludes the extent to which police officers pursue a policy approaching "full" enforcement for all offenses depends on community values. 1 figure