Showing the causal link between community engagement and improved health outcomes is a ‘holy grail’ of health policy. This article argues that this ‘holy grail’ has remained elusive because community engagement in primary health care is under-theorized, having been based on positive a priori assumptions, e.g. that people necessarily want to be engaged in governing their health system. By adopting a theory-driven approach and an agnostic premise, we show that understanding why, how and when community engagement may emerge or function spontaneously is important for informing efforts to support community engagement in primary health care primary health care governance. We draw on empirical research on community engagement in Nigeria and on the literature to identify the ‘why’ (coalition of service users can emerge in response to under-governance); the ‘how’ (five modes: through meetings; reaching out within their community; lobbying governments; augmenting government support; and taking control of service delivery) and the ‘when’ (as geographical, socio-economic and institutional context align, such that the benefits of action outweigh costs). Understanding the broad patterns of mechanisms and of contextual factors that apply across communities is, after all, our ‘holy grail’—and this understanding should inform efforts to tailor support for community engagement in governance in different settings.

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