This research brief is one of a series of six briefs, which provide an overview of available evidence shown in the Campbell-UNICEF Mega-Map of the effectiveness of interventions to improve child wellbeing in low- and middle-income countries (LMICs). Five of the six briefs summarize evidence as mapped against the five Goal Areas of UNICEF's Strategic Plan 2018-2021, although it is anticipated that they will also be useful for others working in the child well-being space. The sixth brief maps the COVID-19-relevant studies. This brief provides an overview of the available evidence related to interventions to ensure that every child lives in a safe and clean environment. The purpose of the research brief is to: (1) Make potential users aware of the map and its contents; (2) Identify areas in which there is ample evidence to guide policy and practice, and so encourage policymakers and practitioners to use the map as a way to access rigorous studies of effectiveness; and (3) Identify gaps in the evidence base, and so encourage research commissioners to commission studies to fill these evidence gaps. [This brief is an update of the 2020 version. It was written with assistance from Yashika Kanojia.]