Parent responsiveness to infants' cues may support attachment, mental health, and neurodevelopment. Across studies, parent responsiveness includes various behaviours (e.g., verbal responses, sensitivity, timeliness, physical proximity). Mixed evidence regarding associations between parent responsiveness and child development may be partially attributable to variable conceptualizations of parent responsiveness. Additionally, divergent perspectives on parent responsiveness may limit cross-disciplinary collaborations, which are important to best support families in developing responsive parenting skills. Thus, the purpose of this systematic review of articles published from 1952 to 2022 was to establish a multidimensional definition of parent responsiveness. Inclusion criteria for the 463 articles included in this review were: (a) primary focus on behavioural parent responsiveness; (b) average infant age 6–18 months; and (c) in-depth definition of parent responsiveness. We completed a qualitative content analysis of the definitions of parent responsiveness extracted from each included article. The resulting definition contains 15 dimensions of parent responsiveness across four levels of behaviour that comprehensively describe the complexity of parent-infant interactions. This model is foundational for future studies of parent responsiveness, its impact on child development, and factors that influence parents' ability to respond to their infants' cues.