Multimorbidity-usually defined as the co-existence of two or more long-term conditions in an individual-is the norm rather than the exception in primary care patients 1, 2 and will become more prevalent as populations age. 3, 1 Multimorbidity cuts across the vertical paradigms in which most health research and policy is envisaged, supported and carried out, reflecting not only specialist interests in particular problems and diseases, but also the tendency of research to focus on easily defined issues.‘‘Complicated’’patients with multimorbidity are usually excluded from such research. Although complexity is under-represented in the research literature, it is common place in general medical practice, where the challenges are ‘‘horizontal’’, integrating not only at the level of the clinical encounter, but also in the co-ordination of services to support patients with multiple problems. The challenge of carrying out research on multimorbidity is to reflect, investigate, inform and improve these aspects of generalist clinical practice.

Given that multimorbidity is a challenge facing practitioners and patients alike it has attracted surprisingly little research interest. 4 The research to date has largely focussed on analysis of the impact of multimorbidity on individuals and healthcare systems, with very few studies examining interventions to improve outcomes. 5 One of ‘multimorbidity’s many challenges’1 includes setting a research agenda to systematically begin to answer important practical issues in supporting people with multimorbidity. Given the scale and complexity of the task, the first difficulty is simply knowing where to start.