The day fine involves a simple 2-step process in setting fine amounts that embraces the principles of proportionality and equity. First, the court sentences the offender to a certain number of day fine units, according to the gravity of the offense, but without regard to his or her means. Second, the value of each unit is set at a share of the offender's daily income. While admittedly less severe than incarceration, the day fine has a punitive impact on the offender. Recent research indicates that imposing fines as punishment may also enhance deterrence. The day fine project in Staten Island was limited to the trial court of limited jurisdiction. A sample of penal code cases disposed of in the court during a 6-month period was studied to determine the range of penal code charges commonly handled by the court. Each offense was then assigned a presumptive number of day fine units, ranging from a low of 5 units for a minor offense to a high of 120 for a severe offense. Each offense was provided with "discount" and "premium" units to give additional flexibility and encourage judicial discretion in accounting for mitigating or aggravating circumstances of individual cases. Much of the needed basic income information for determining the offender's ability to pay was already available to the court at sentencing. Appropriate timeframes for payment were established as well as enforcement measures such as warning letters, direct telephone contact, and the threat of jailing for default. Illustrations of typical offenders receiving day fines are presented. The impact of day fines on sentencing practices and the level of day fine revenues are discussed. 33 footnotes and 8 tables