Although classical theorists tend to believe that immigrant youth are more delinquent than native-born adolescents, the existing empirical studies have shown the opposite. The current paper first gives a comprehensive overview of major theoretical explanations for the relatively lower level of delinquency among immigrant youth, including cultural perspectives, strain theories, social control theory, social learning theory, and social disorganization theory. The main argument is that immigrant youth who have not yet acculturated to the youth subculture of the host society are more law-abiding due to protections from their traditional traits (i.e., being more realistic, stronger ties with family/schools, less access to delinquent friends, and higher level of collective efficacy in homogeneous neighborhoods). All these theories are also applied to explain the generational differences in terms of delinquency: compared to earlier generations, later generations of immigrant youth are often more delinquent because they are more acculturated and the protective factors from their origins wear off over time. The continuing public and political bias toward immigrant youth has been explained by social constructionists. We further discuss the necessity of a synthesis of these theoretical approaches and the importance to examine both internal and international migration under similar theoretical frameworks in the modern era.