 Life-course research is an interdisciplinary approach to understanding how biology and environment interact to influence health outcomes throughout the lifespan. It recognises the complexity of health development and seeks to understand the dynamic interactions between genetics and environment. Complex systems science provides a framework for exploring these interactions by decomposing them into component parts and examining the reciprocal relationship between individuals and their environment. This framework has been applied to clinical and translational research domains, such as precision medicine and personalised healthcare, to identify key questions and recommendations for future research. This article was authored by Heidi A. Hansen, Claire L. Leeser, Gretchen Bandaly, and others.