The communities and neighbourhoods where we grow up have a lifelong influence on the illnesses we get and how long we live. Health is about avoiding disease and having a long life, but is also about feeling well in mind and body, feeling safe, being part of a community and having things to look forward to. Many aspects of the world around us influence our health directly or influence health related behaviours. These so called "broader" determinants of health include the houses and flats we live in, the design of our roads and high streets, the availability and quality of parks, green spaces, libraries, galleries, museums, sports and recreational facilities, entertainment opportunities, places and events to connect with others, the shops and businesses around us, pollution levels, learning opportunities, the jobs available to us and whether we have enough money to make ends meet and to participate in social activities. Attempts to change health related behaviours such as unhealthy eating, drinking, smoking and lack of exercise, have met with important but limited success. For example, increased awareness of links between childhood obesity and ill health and the importance of exercise and healthy diet will have limited success if broader determinants are not also tackled. These broader determinants include, but are not limited to, the many fast food outlets that children may walk past, lack of access to high quality play and recreational facilities, sell off of school playing fields, streets that are not safe for children to walk or cycle to school, lack of high quality green spaces for exercise, shops with poor choice of healthy foods, increased screen time replacing physical activity, poor quality of school food, and, for some, insufficient income to buy healthy food. Our ActEarly approach focuses on improving the health of children in two contrasting areas with high levels of child poverty, Bradford in Yorkshire and Tower Hamlets in London. In preparation for this work we have worked with local communities, local authorities and other local organisations and have established shared priority areas for research: Healthy Places, Healthy Learning and Healthy Livelihoods. We have brought together experts in these themes with local community and local authority representatives to begin to develop a range of approaches to improving child health across these areas. For example, within our Healthy Places theme we will work together to: map local community assets and to understand how they can be improved and used by more people; develop a Healthy Streets approach and improve green space quality. In our Healthy Learning theme we will work together to develop local "Evidence Active Networks" of pre-school, school and community learning venues. These networks will help develop and evaluate a wide range of approaches to improve child health. In our Healthy Livelihoods theme we will work together on approaches such as relocation of welfare advice services to improve access, enabling parental leave, ensuring a minimum basic income in school leavers, providing life skills training and involving local communities in decisions on how to spend local authority budgets. To understand the effect of these approaches on child health we will develop strong data resources that bring together existing information from across our localities to measure changes in the local environment, health related behaviours and health outcomes. Teams of researchers will use this data and work with local communities to understand how successful our initiatives have been. We describe our emphasis on early life interventions, our highly collaborative approach and development of local data sources to enable evaluation of multiple initiatives, as the "ActEarly Collaboratory". We hope the approach will promote a fairer and healthier future for children and a global example of how to work with communities to improve health.