["Developmental Science, Volume 29, Issue 4, July 2026. ", "\nABSTRACT\n\nCoordination of caregivers’ (N = 50, five fathers and 45 mothers) and 9‐month‐old infants’ (15 girls, 34 boys, one not reported) gaze during naturalistic play with a puzzle and activity board was examined using the Actor–Partner Interdependence Model within a Dynamic Structural Equation Modeling framework. This approach allows for the simultaneous estimation of each partner's effect on their own subsequent looking and on their partner's subsequent looking. Analysis of gaze data from head‐mounted eye trackers worn by North American, middle‐class, racially and ethnically diverse caregivers and infants (21 infants and 25 parents were White and not Hispanic; the remaining identified as Asian, Black, Multiracial, or another race, and/or as Hispanic) revealed that infants’ and caregivers’ looks at a moment was related both to their own subsequent looks and to their partners’ subsequent looks. Moreover, infants’ looks to their parents’ faces more strongly predicted parents’ subsequent looks to their infants’ faces than the reverse, suggesting that mutual gaze was primarily driven by infants’ attention. In contrast, there was no difference in infants’ or parents’ influence on their partners’ looking at objects, indicating that joint attention emerged through mutual coordination. Furthermore, there was a stronger effect of gaze on subsequent gaze for infants than for parents, suggesting that infants’ attention was more sustained and less flexible than that of their caregivers. This work highlights the co‐constructed nature of the moment‐to‐moment coordination of attention between caregivers and infants.\n\n\nSummary\n\nWe applied the Actor–Partner Interdependence Model within Dynamic Structural Equation Modeling to capture second‐by‐second coordination of attention between caregivers and their 9‐month‐old infants.\nWe replicated in two naturalistic play settings that infants rarely look at parents’ faces and look more towards objects than caregivers.\nWe demonstrated that parents and infants influence each other's subsequent in‐the‐moment attention during episodes of mutual gaze and joint attention.\nMutual gaze was primarily infant‐driven, whereas object‐focused joint attention was reciprocal between partners; infants also showed “stickier” attention than caregivers.\n\n\n"]