An enhanced role for primary health care (PHC) is currently a matter of political priority in the UK. This higher profile is drawing attention to a range of unresolved challenges and issues, relating to both the structure and content of provision, which currently permeate the system. Running in parallel with this is a recognition that: to date, PHC has been under-researched; that, as a result, our understanding of it is frequently poor; and that, as a consequence, fresh perspectives are needed in order to effectively research this uncertain, evolving and increasingly important healthcare sector. In this paper we argue that social worlds theory (SWT) provides, albeit in a suitably modified form, an ideal conceptual framework for the analysis of contemporary primary care. SWT is an approach which assumes complexity and constant evolution, and its core concepts are directed towards unravelling the consequences of encounters between different interest groups--something which is of particular utility at this time given the increasing attention to user participation, and an ongoing questioning of established patterns of professional authority. It is an approach which has rarely been employed empirically, even beyond medicine. In order to illustrate the wide relevance of the approach, we discuss how it can facilitate research at all levels of PHC: i.e., in relation to aspects of medical practice (the case of medically unexplained symptoms); shifts in service organisation (changing professional roles and the introduction of policy reforms); and issues which straddle both organisation and content (the increasing use of complementary medicine in primary care). In each case the approach is able to embrace the complexity of situations characterised by the intersection of professional and lay social worlds and is able to provide the conceptual tools through which resultant processes can be tracked and investigated.