--- - |2+ Abstract Power processes in siblings' and friends' conflict interactions are of significance for children's development and socialization. This study conducted a comparative analysis of power behaviours (resources and effectiveness) utilized by dyadic partners in sibling and friend conflict during early childhood when focal children were aged 4. The sample consisted of 65 families and included 347 sibling conflict sequences and 326 friend conflict sequences. Data based upon naturalistic observations were coded for resources of power and power effectiveness. Patterns of findings were identified in the conflict process. Specifically, dyads used simple demands most often, followed by coercive, then elaborated information, and finally questioning power. Despite similarities, sibling dyads used coercive power and negative reward power more often than friends. Regarding power effectiveness, sibling and friend dyads were most effective using coercive power, followed by elaborated, and then questioning power. These findings provide strong support for the importance of taking the dyadic relationship context into account when studying the power process in children's interactions. Highlights How does siblings' and friends' dyadic use of power resources and effectiveness differ in the process and outcome of conflict in early childhood? Data were based upon naturalistic observations of conflict, and findings provide strong support for dyadic analyses when studying the power process in siblings and friends interactions. The findings provide new and novel insights regarding children's agency in conflict, thus highlighting the contributions of children to their own socialization process. - Infant and Child Development, Volume 27, Issue 4, July/August 2018.