Numerical guidelines are promulgated by a sentencing commission through a sentencing grid that scores offenders, with an offender's score determining the sentence received. Numerical guidelines reflect a sentencing rationale (e.g., punishment based on offense severity and/or criminal history), penalties according to rationale factors, and an effort to control prison populations. Numerical guidelines provide a precise mechanism for implementing a consistent sentencing rationale and controlling prison populations, but its mechanistic approach can magnify flaws in the scoring system that would be modified in a more flexible approach. Narrative guidelines consist of statements of sentencing principles applied by sentencing courts and interpreted in appellate case-law. England has entrusted the development of such principles to the Court of Appeal. Finland and Sweden state sentencing principles in legislation, with Sweden providing the courts more detailed guidance than does Finland. The success of narrative guidelines requires the drafting of principles by a skilled body, perceptive interpretation by appellate courts, responsive sentencing courts, and continuous analysis of the impact of sentencing on prison crowding. 15 notes and 13 references.