This paper reports on the systematic search and review of the literature relating to the health and wellbeing of young children across the transition to school. It identified 56 papers (including empirical studies, reviews, commentaries, and reports) relevant to the research questions and completed an interpretive systematic review to ascertain the current state of the literature. The review employed the Critical Interpretive Synthesis (CIS) method to allow for a rigorous and systematic review of a disparate literature which stretches across several disciplines. The findings are presented in seven thematic categories: current conceptualisations of health and wellbeing, assessment and measurement, 'school readiness', service integration, transition actors, 'at risk' children, and child voice. These findings illustrate the ways in which concepts have been constructed, identified, and operationalised in early years research, practice, and policy. Moreover, it highlights that 'what is known' can be used to inform the review or implementation of services, practices, and partnerships that support child health and wellbeing during the transition to school.