Despite significant successes in controlling a number of communicable diseases in low and middle income countries, important challenges remain, one being that a large proportion of patients with conditions of public health significance, such as tuberculosis, malaria, or sexually transmitted diseases, seek care in the largely unregulated 'for profit' private sector. Private providers (PPs) often offer services which are perceived by users to be more attractive. However, the available evidence suggests that serious deficiencies in technical quality are often present. Evaluations of interventions to promote evidence-based care in high income countries have shown that multi-faceted strategies which increase provider knowledge have had some success in improving service quality. A wider range of factors needs to be considered in low and middle income countries (LMICs), especially factors which contribute to discrepancies between provider knowledge and practice. Studies have shown that PPs, especially, perceive or experience patient and community pressures to provide inappropriate treatments. LMIC governments also lack the capacity to enforce regulatory controls. Context-specific multi-faceted strategies are needed, including the local adaptation and dissemination to providers of relevant evidence, the education of patients and communities to adopt effective treatment-seeking and treatment-taking behaviour, and feasible mechanisms for ensuring and monitoring service quality, which may include a role for self-regulation by provider organizations or provider accreditation. Developing, implementing and evaluating strategies to improve the quality of service provision will depend on the involvement of the key stakeholders, including policy makers and PPs. Focusing on studies from Asia, Africa and Latin America, this paper develops a model for identifying the influences on PPs, mainly private medical practitioners, in their management of conditions of public health significance. Based on this, multi-faceted strategies for improving the quality of treatment provision are suggested. Interventions need to be inexpensive, practical, efficient, effective and sustainable over the medium to long term. Achieving this is a significant challenge.