The term “delinquency” is defined from both a criminal law and a status offense perspective, as well as from a social and criminological standpoint. The ever-shifting definition of juvenile delinquency is underscored and the understanding of juvenile delinquency as a continuum of behaviors is explained. Legal definitions of “juvenile” and the use of transfers or waivers to adult courts are presented by State. The prevalence and characteristics of delinquency in the United States are measured through many different methods, including official measures of delinquency such as the Federal Bureau of Investigation’s Uniform Crime Reports program and juvenile court and corrections statistics, as well as through self-report measures of delinquency generally derived from questionnaires filled out by student and juvenile delinquency populations. Statistics on juvenile delinquency in the United States derived from each type of measurement are presented, which illustrate trends in juvenile crimes; age, sex, and race distributions of juvenile offenders; and the characteristics of juveniles housed in correctional facilities. Self-report juvenile delinquency measures are critiqued and comparisons of the different delinquency measures are presented. Three discussion questions at the end of the chapter focus attention on the varying definition of delinquency and the different types of delinquency measures. Key terms are listed. Figures, tables