Most criminological theories predict an inverse relationship between employment and crime, but teenagers' involvement in paid work during the school year is correlated positively with delinquency and substance use. Whether the work-delinquency association is causal or spurious has been debated for a long time. This study estimates the effect of paid work on juvenile delinquency using longitudinal data from the national Monitoring the Future project. The authors address issues of spuriousness by using a two-level hierarchical model to estimate the relationships of within-individual changes in juvenile delinquency and substance use to those in paid work and other explanatory variables. They also disentangle the effects of actual employment from the preferences for employment to provide insight about the likely role of time-varying selection factors tied to employment, delinquency, school engagement, and leisure activities. Whereas causal effects of employment would produce differences based on whether and how many hours respondents worked, the study found significantly higher rates of crime and substance use among nonemployed youth who preferred intensive versus moderate work. The study findings suggest the relationship between high-intensity work and delinquency results from preexisting factors that lead youth to desire varying levels of employment. Tables and references (Published Abstract)