The aim of this study was to investigate if children's early responsiveness toward social partners is developmentally related to their growing concept of self, as reflected in their mirror self-recognition (MSR) and delayed self-recognition (DSR). Thus, a longitudinal study assessed infants' responsiveness (e.g.,smiling, gaze) toward social partners during the still-face (SF) task and a social imitation game and related it to their emerging MSR and DSR. Thereby, children were tested at regular time points from 9 months to 4 years of age. Results revealed significant predictive relations between children's responsiveness toward a social partner in the SF task at 9 months and their MSR at 24 months. Further, interindividual differences in children's awareness of and responsiveness toward being imitated in a social imitation game at 12 months proved to be the strongest predictor of children's DSR at 4 years, while some additional variance was explained by MSR at 24 months and verbal intelligence. Overall, findings suggest a developmental link between children's early awareness of and responsiveness toward the social world and their later ability to form a concept of self.