Breastfeeding in UK Pakistani and Bangladeshi communities is positively and negatively influenced by cultural beliefs and practices. The LIFT (Learning about Infant Feeding Together) project aimed to understand the determinants of infant feeding in these target communities and to engage them in the development of a culturally specific and acceptable infant feeding intervention to support breastfeeding. Reported here is phase one of the LIFT project guided by the REPLACE approach (a framework for the development of community-based interventions). The project involved an initial lengthy period of engagement with the target communities, using methods such as a community outreach event and identification of community peer group champions to help build trust. This was followed by iterative community workshops used to explore and build an understanding of infant feeding practices and the social norms and beliefs underlying these, and to assess community readiness to change. Consistent with previous research, the six key practices and beliefs identified from the workshops were: (1) Disparities between personal views versus cultural and normative barriers, (2) Family relationships and the influence on infant feeding decisions, (3) Pardah (modesty) and being unable to breastfeed in front of others, (4) Discarding colostrum (first breast milk), (5) Pre-lacteal feeds (feeds within a few hours of birth and before any breast or formula milk has been given) and complementary feeding before the baby is 6 months old, and (6) The belief that bigger babies are better and that formula helps babies to grow. Participants perceived that Pakistani and Bangladeshi communities would be amenable to intervention that aimed to change some but not all of the infant feeding behaviours identified. Findings informed the co-development of a culturally appropriate intervention toolkit to optimise infant feeding behaviour.