Understanding male engagement in child health and nutrition in urban informal settlements: A formative participatory exploration Improving child health requires primary prevention, quality health services and community action to address the underlying drivers of health and wellbeing. Whilst there is recognition that the health system encompasses both the suppliers of policy, services, and interventions, and the communities and households intended to benefit from them; in health systems research the focus has primarily been on the supply-side with little attention given to the demand-side of this equation.  Gender roles and relations play an important role in child health and nutritional status. In many sub-Saharan African (sSA) settings, childcare and health is predominantly a female domain with men largely absent or only involved in perceived severe or serious cases. Similarly, intentionally or unintentionally, child health programmes in sSA countries predominantly focus on women. While women are perceived as responsible for children, paradoxically they must negotiate decision-making and resources with other family members, including men. By exclusively focusing on women without considering family dynamics or the broader social context, these programmes may inadvertently reinforce harmful gender divisions and practices related to child health and nutrition. Evidence suggests that programmes targeting women might be more effective if men's roles are considered and transformed to affirm more equitable gender relations. For example, in the 'Men in Maternity' programme in New Delhi, India, husbands were encouraged to play an active role in their wives' antenatal and post-natal care with improved outcomes in the intervention compared to the control groups. Similarly, the IMAGE intervention in Limpopo South Africa used a participatory approach to engage men and challenge behaviours in relation to intimate partner violence and HIV transmission; resulting in a significant reduction in the risk of physical and sexual violence by an intimate partner even up to two years after introduction of the intervention.   Informal settlements (referred to colloquially as 'slums') house a significant proportion of the world's urban population particularly in low- and middle-income countries; with this number set to rise with increasing urbanization. Throughout their life-course, these populations suffer from disproportionately higher burden of illness compared to the general population. In Kenya where this work will be undertaken, studies show that slums in the capital city of Nairobi have higher child and under-five mortality rates compared to the national, urban and rural averages with long and complex pathways to seeking care; frequently involving the use of informal systems of healthcare prior to, or concurrently with, engaging formal health facilities. Furthermore, following treatment in the formal health system, ill or recovering children are 'discharged back' into their homes and communities. Without proper understanding of the complexities and dynamics operating at the household and community levels, hospital-initiated interventions are likely to be less effective and sustainable.  Focusing on the demand-side of the health system, the proposed work seeks to answer if and how participatory approaches can strengthen male involvement in child health and nutrition for better outcomes. Specifically:1) To understand men's and women's perspectives of the actual, desired and perceived role of men in child health, and related barriers and facilitators; and 2) Use an in-depth participatory approach to engage men and other stakeholders in co-creating a context-specific, feasible, and scalable male engagement intervention package for improved and more responsive health service delivery. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.