Born in Bradford (BiB) includes two multi ethnic and socially diverse birth cohort studies. Bib, now ten years old, is an observational longitudinal study involving 13,500 children. Born in Bradford Better Start (BiBBS), currently in its second year of recruitment, is an experimental birth cohort study aimed at understanding what helps families with small children in Bradford, UK to live healthier and happier lives. Successful engagement from all communities is important to ensure representation in research for comparative analysis. Effective community engagement is a crucial part of our work to ensure we overcome some of the challenges faced in engaging communities in our research such as language, trust and interest. National Institute for Health and Care Excellence (NICE) guidelines on Community Engagement has advice about local based approaches to improve health and wellbeing that include building local assets. We have developed an approach to identify community readiness for the initiatives we wish to introduce, community engagement to offer input on research strategy and on routes to implementation, and extensive activities to keep cohort members informed and involved. The development of a community engagement policy offering a wide range of community engagement methods has resulted in changes in practice, it has embedded knowledge about our communities into all we do and it has helped ensure continuing enthusiasm from cohort members for our studies. We report on how we assess community readiness and the impact this has on study and service design, on how community engagement has prompted changes of emphasis in our studies and on the challenges of reconciling research agendas and community wishes. Additionally, we consider the impact of ethnicity and migration on the ways we seek to reach and learn from our communities.