The feeding of human milk to socially and biologically unrelated infants is not a new phenomenon, but the Euroamerican values of individualism have generated expectations that mothers are individually responsible for feeding their own infants. Using a bio-communities of practice framework, this dynamic new analysis explores the emotional and material dimensions of the growing milk sharing practice in the Global North and its implications for contemporary understandings of infant feeding in the US. Ranging widely across themes of motherhood, gender and sociology, this is a compelling empirical account of infant feeding that stimulates new thinking about a contentious practice.The motivations and wider meanings of peer breast milk sharing are revealed in this thought-provoking empirical analysis. Using a bio-communities of practice framework the authors explore the emotional and material dimensions of the practice and its implications for contemporary understandings of infant feeding in the US, providing new insights into a contentious topic.