Interprofessional teamwork has become an integral feature of healthcare delivery in a wide range of conditions and services in many countries. Many assumptions are made in healthcare literature and policy about how interprofessional teams function and about the outcomes of interprofessional teamwork. Realist synthesis is an approach to reviewing research evidence on complex interventions which seeks to explore these assumptions. It does this by unpacking the mechanisms of an intervention, exploring the contexts which trigger or deactivate them and connecting these contexts and mechanisms to their subsequent outcomes. This is the second in a series of four papers reporting a realist synthesis of interprofessional teamworking. The paper discusses four of the 13 mechanisms identified in the synthesis: collaboration and coordination; pooling of resources; individual learning; and role blurring. These mechanisms together capture the day-to-day functioning of teams and the dependence of that on members' understanding each others' skills and knowledge and learning from them. This synthesis found empirical evidence to support all four mechanisms, which tentatively suggests that collaboration, pooling, learning, and role blurring are all underlying processes of interprofessional teamwork. However, the supporting evidence for individual learning was relatively weak, therefore there may be assumptions made about learning within healthcare literature and policy that are not founded upon strong empirical evidence. There is a need for more robust research on individual learning to further understand its relationship with interprofessional teamworking in healthcare.

Background: The realist approach is a form of theory-driven evaluation developed to strengthen the explanatory power of evaluation studies and contribute to evidence-based policy and practice. It is a generic approach that can be applied to many fields of research, including health and social care. Content: This article introduces the reader to the realist approach and outlines its application in empirical evaluation studies and literature syntheses. It describes how the realist researcher evaluates complex social interventions not by asking whether a particular programme or intervention ‘works’, but, recognising that all interventions only ever work for certain people in certain circumstances, by asking instead ‘what works for whom in what circumstances’? Realist researchers then try to articulate the theories (termed ‘mechanisms’) that underpin the programme and explore how contexts influence the mechanisms to produce different programme outcomes. Conclusions: Realist evaluation and realist synthesis are an advanced approach to evaluation research, but they offer an innovative and insightful means by which to further our understanding of complex social interventions.

Realist synthesis offers a novel and innovative way to interrogate the large literature on interprofessional teamwork in health and social care teams. This article introduces realist synthesis and its approach to identifying and testing the underpinning processes (or "mechanisms") that make an intervention work, the contexts that trigger those mechanisms and their subsequent outcomes. A realist synthesis of the evidence on interprofessional teamwork is described. Thirteen mechanisms were identified in the synthesis and findings for one mechanism, called "Support and value" are presented in this paper. The evidence for the other twelve mechanisms ("collaboration and coordination", "pooling of resources", "individual learning", "role blurring", "efficient, open and equitable communication", "tactical communication", "shared responsibility and influence", "team behavioural norms", "shared responsibility and influence", "critically reviewing performance and decisions", "generating and implementing new ideas" and "leadership") are reported in a further three papers in this series. The "support and value" mechanism referred to the ways in which team members supported one another, respected other's skills and abilities and valued each other's contributions. "Support and value" was present in some, but far from all, teams and a number of contexts that explained this variation were identified. The article concludes with a discussion of the challenges and benefits of undertaking this realist synthesis.

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