The future of public health policymaking after COVID-19: a qualitative systematic review of lessons from Health in All Policies.

: 'Health in All Policies' (HiAP) describes the pursuit of health equity. It has five main elements: treat health as a human right; identify evidence of the 'social determinants' of health inequalities, recognise that most powers to affect health are not held by health departments, promote intersectoral policymaking and collaboration inside and outside of government, and generate political will. Studies describe its potential but bemoan a major implementation gap. Some HiAP scholars learn from policymaking research how to understand this gap, but the use of policy theories is patchy. In that context, our guiding research question is: It allows us to zoom-out to survey the field and zoom-in to identify: the assumed and actual causes of policy change, and transferable lessons to HiAP scholars and advocates.  Our qualitative systematic review (two phases, 2018 and 2020) identified 4972 HiAP articles. Of these, 113 journal articles (research and commentary) provide a non-trivial reference to policymaking (at least one reference to a policymaking concept). We use the 113 articles to produce a general HiAP narrative and explore how the relatively theory-informed articles enhance it. : Most articles focus on policy analysis (identifying policy problems and solutions) rather than policy theory (explaining policymaking dynamics). They report a disappointing gap between HiAP expectations and policy outcomes. Theory-informed articles contribute to a HiAP playbook to close that gap or a programme theory to design and evaluate HiAP in new ways.   : Few HiAP articles use policy theories for their intended purpose. Policy theories provide lessons to aid critical reflection on power, political dilemmas, and policymaking context. HiAP scholars seek more instrumental lessons, potentially at the cost of effective advocacy and research.