The past two decades have seen a steady growth in attention to the private sector role within the overall health systems of lowand middle-income countries. Since the 1990s researchers have worked to call attention to the previously unrecognized scale of private medical services in the developing world (Berman and Rose 1996; Brugha and Zwi 1998; Hanson and Berman 1998; Preker et al. 2000; Uplekar 2000; Berman 2001; Mills et al. 2002; Harding and Preker 2003). As cross-country datasets have become available, the evidence has become increasingly clear that the private sector plays a major role in financing and provision of care in low-and middle-income countries (LMICs)(Zwi et al. 2001; Ha et al. 2002; Liu et al. 2006; Konde-Lule et al. 2010). In parallel, a half-dozen multi-centre projects supporting research on the private sector in LMICs have been implemented (De Costa and Diwan 2007; Access Health International, nd; PSP, nd; PSP-One, nd; Results for Development Institute, nd). Evidence and analysis has also pointed to the challenges and opportunities that the private sector poses to health and health sector development (Lonnroth et al. 1998; Lonnroth et al. 2001; Travis and Cassels 2006). The result of this growth in evidence is a general acknowledgement of the private sector and acceptance of its existence and important role in health care for many people in low-and middle-income countries. Consequently, the focus in research and policy development has moved from measurement to nuanced assessment of policy options and interventions for engagement of the private sector in public policy goal attainment (Montagu 2002; De Costa et al. 2008; Dimovska 2009; Lagomarsino 2009; Kangwana et al. 2011). As a result, in 2010 the World Health Assembly passed a resolution calling on countries to ‘constructively engage the private sector in providing essential health-care services’(WHO 2010). The British development agency, DFID(Department for

International Development), has supported a series of recent systematic reviews addressing voucher-based payments for care, the quality of private provision, and health outcomes in public vs private facilities in LMICs (Madhavan 2010; Montagu 2010; Meyer 2011). Health system thinking is increasingly acknowledging, and measuring, the scale of private provision. While documentation and guidance on policies and analysis are still in limited supply, the field is expanding. A further indication of this is the growing body of researchers addressing issues of private health care in LMICs and sharing their evidence in public fora and in peer-reviewed journals. In 2007 an informal gathering of researchers on the private sector met for lunch at the VIth World Congress of the International Health Economics Association (iHEA) in Copenhagen. From this group a small committee was formed to organize a symposium on the Role of the Private Sector in Health Care in conjunction with the 2009 VIIth iHEA congress. Around 100 participants attended the symposium. The papers in this supplement were presented at that 2009 Symposium. They are indicative of the growing sophistication and depth of research being conducted on issues of private health care provision in LMICs.