The present study is focused on anger expression and regulation within the National Institute of Mental Health (NIMH) Research Domain Criteria (RDoC) construct of Frustrative Nonreward. Although previous studies have examined associations between child anger regulation and expression, these studies do not directly address the dynamic processes involved in Frustrative Nonreward using microlongitudinal methods. The current study used data from 561 adopted children, their adoptive parents, and birth parents and aimed to address gaps in the literature by examining: (a) temporal associations between anger expression during a frustrating situation, and behaviors thought to regulate emotions (e.g., attempt-to-escape, support-seeking, distraction, and focus-on-restraint) on a microlongitudinal scale during an arm restraint task assessed at 27 months; (b) birth parent externalizing problems and overreactive parenting by adoptive parents as predictors of child anger expression and moderators of the moment-to-moment associations estimated in Step 1; and (c) longitudinal associations (linear vs. quadratic) between anger expressions and externalizing behaviors at 4.5 years. Findings indicated that children's attempt-to-escape and support-seeking predicted an increase in anger expression in the following 3-s interval, whereas distraction and focus-on-restraint were not associated with changes in anger expression. Furthermore, we found that birth parents' externalizing problems were significantly associated with child anger expression, suggesting heritable influences. Anger expression showed a U-shaped longitudinal association with paternal report of externalizing behaviors at 4.5 years. Taken together, the findings emphasize the significance of integrating microlongitudinal analysis approaches into the RDoC framework, helping to advance our understanding of dynamic processes underlying reactions to Frustrative Nonreward. (PsycInfo Database Record (c) 2022 APA, all rights reserved).