Creating an optimal start during the first 1,000 days of children is an important focus for researchers and policy makers. Parents can positively influence child development through sensitive... Show moreCreating an optimal start during the first 1,000 days of children is an important focus for researchers and policy makers. Parents can positively influence child development through sensitive parenting, which is the ability to understand and promptly and adequately respond to a child’s signals. This thesis provides insight in the development of sensitive parenting from infancy to toddlerhood in primiparous mothers and fathers through longitudinal data from the Netherlands, United Kingdom, and United States. The results demonstrate that fathers and mothers respond more sensitively to their baby in more ecologically valid contexts, i.e. during situations more representative of their daily reality, than in less ecologically valid contexts. Therefore, we recommend to take context into account when parenting skills are studied and evaluated. Next, we made a first step towards clarity on the way parents reflect on the parent-child relationship during the transition to parenthood and in relation to parental sensitivity. We found weak evidence for the theorized link between this reflection and parental sensitivity. Finally, we found that mothers and fathers are equally sensitive across the first two years, and sensitivity levels during this period increase in both parents, indicating that mothers and fathers actually do become better in sensitive parenting. Show less