Previous studies have identified three central pathways of parent-to-child anxiety transmission: (1) shared genetic load, (2) fetal programming through maternal experiences during pregnancy, and (3) parental behaviors that model and shape anxiety-linked cognitive, behavioral, and emotional profiles. To date, we have few tractable mechanisms by which we can intervene upon the first two pathways. However, a wide and robust literature has characterized specific parenting behaviors linked to the emergence of childhood anxiety, making it a translatable target. Much of this literature has focused on broad profiles based on questionnaire measures or aggregate summaries of behaviors averaged over time. As a result, we know little regarding the moment- by-moment interactions that serve as a behavioral conduit for intergenerational transmission. Repeated daily interactions with caregivers, channeled through dyadic social dynamics, attune the child to parental expressions of fear and distress influencing the child's own responses to surrounding events. The current longitudinal study will focus on two instances of dyadic social dynamics as mechanisms for anxiety transmission. First is dyadic synchrony, a process captured in the temporal co-ordination of discrete microlevel signals between dyadic partners evident across levels of analysis. Second is emotion modeling, in which observed patterns of parental emotion, distress, and coping are internalized by the child, supported by psychophysiological synchrony, and then reflected in their own subsequent behavior. Children ages 4 to 6 and their parent, including both mothers and fathers, will be assessed at five time points, 6 months apart in a multi- modal battery. Parent-child dyads will engage in mildly stressful interactions that allow us to capture neural (fNIRS), psychophysiological (RSA), attentional (mobile eye-tracking), and behavioral (overt emotion and distress) patterns of synchrony. In addition, we will assess regulatory (EEG delta-beta coupling), cognitive (ERP N2 component), and attentional (threat bias) markers of socioemotional development and anxiety risk. Finally, we asses child fearful temperament, which is associated with greater sensitivity to the social environment and the later emergence of anxiety. Thus, we can ask (1) Concurrently, how do patterns of dyadic social dynamics vary across parent-child pairs? (2) Across tasks, to what extent does variation in dyadic patterns help predict anxiety risk? (3) Over time, can we predict socioemotional profiles and anxiety risk from earlier patterns of dynamic dyadic interactions? Reflecting the Research Domain Criteria, we integrate multilevel mechanisms by examining how social and arousal/regulatory systems are coupled through dyadic social dynamics to influence the emergence of anxiety via the cognitive (attention to threat, cognitive control), arousal/regulatory (delta-beta coupling), and negative valence (fearful temperament) systems. In doing ...