Youth antisocial behavior (AB; lying, aggression, rule-breaking) is a major public health concern due to its high prevalence and harmful consequences. Recent research has suggested that youth with AB are a heterogeneous group, which may undermine intervention success. For instance, elevated callous-unemotional (CU) traits are associated with more severe and persistent AB. Moreover, CU traits are a downward extension of psychopathic traits, and are a risk factor for adult psychopathy. Previous work suggests that the combination of AB and elevated CU traits may be etiologically distinct from AB alone. However, previous research has often been limited by the use of case-control designs in highly specialized populations, at severe levels of both AB and CU traits (e.g., adjudicated, clinical or criminal). This dissertation is comprised of three studies that examine developmental trajectories and neurocognitive deficits of AB versus CU traits, in community populations, across varying levels of AB and CU traits. To better understand developmental precursors of CU traits, Study 1 examines associations among parental psychopathic traits, parenting practices, and offspring CU traits in adolescence, using a genetically-informed design. Parental interpersonal-affective psychopathic traits were associated with adolescent CU traits and parenting (increased conflict, reduced involvement). Moreover, increased conflict and reduced involvement partially explained associations between parental interpersonal-affective traits and adolescent CU traits. Finally, using a twin difference design, we confirmed that adolescent CU traits were significantly impacted by non-shared environmental parenting influences (increased conflict, reduced involvement). Study 2 identifies neurocognitive deficits associated with the combination of AB and CU traits, in contrast to AB alone. Neither AB, nor CU traits alone, were associated with cognitive functioning when accounting for demographic factors. However, AB and CU traits interacted to predict reaction time variability. At low levels of CU traits, AB was associated with higher reaction time variability (traditionally thought to reflect worse sustained attention). At high levels of CU traits, antisocial behavior was associated lower reaction time variability (thought to reflect better sustained attention). Finally, Study 3 examines patterns of neural network connectivity underlying psychopathic traits in young adulthood using a person-specific approach and determines whether specific features of psychopathy are characterized by distinct network features. There was significant heterogeneity in neural networks of participants, which were characterized by person-specific connections and no common connections across the sample. Psychopathic traits, particularly affective traits, were associated with connection density between the default mode network and central executive network, such that greater density was associated with elevated psychopathic traits. The general discussion chapter of this dissertation highlights the implications of this research for intervention approaches, empirical considerations, and future directions.