The popularity and benefits of social marketing partnerships accord partnerships as the 5th 'P' of the social marketing mix and an essential element of interventions. Yet the scope and substance of partnerships within social marketing remains ambiguous and is an underutilized marketing mix tool. This article critically examines over 50 years of social marketing academic literature to uncover and unpack the full potential of social marketing partnerships and the various forms taken. Periodization is applied as a lens and method for modelling partnership evolution over time. Three dominant eras of social marketing partnerships are evident; the period of transaction, the period of formalization and the period of integrated systems, each with different partnership understandings and characteristics. By examining social marketing partnerships as an evolving entity, this article identifies a 'constant flux' trajectory, with partnerships continuing to respond and react to broadening environmental and theoretical catalysts with the development of a model of social marketing partnerships in sight.