Considerable effort has been made in recent years to gain a better understanding of the effectiveness of different interventions for supporting breastfeeding. However, research has tended to focus primarily on measuring outcomes and has paid comparatively little attention to the relational, organizational, and wider contextual processes that may impact delivery of an intervention. Supporting a woman with breastfeeding is an interpersonal encounter that may play out differently in different contexts, despite the apparently consistent aims and structure of an intervention. We consider the limitations of randomized controlled trials for building understanding of the ways in which different components of an intervention may impact breastfeeding women and how the messages conveyed through interactions with breastfeeding supporters might be received. We argue that qualitative methods are ideally suited to understanding psychosocial processes within breastfeeding interventions and have been underused. After briefly reviewing qualitative research to date into experiences of receiving and delivering breastfeeding support, we discuss the potential of theoretically informed qualitative methodologies to provide fuller understanding of intervention processes by focusing on three examples: phenomenology, ethnography, and discourse analysis. The paper concludes by noting some of the epistemological differences between the broadly positivist approach of trials and qualitative methodologies, and we suggest there is a need for further dialog as to how researchers might bridge these differences in order to develop a fuller and more holistic understanding of how best to support breastfeeding women.