This paper aims to describe and explain the development of third sector primary care organisations in New Zealand. The third sector is the non-government, non-profit sector. International literature suggests that this sector fulfils an important role in democratic societies with market-based economies, providing services otherwise neglected by the government and private for-profit sectors. Third sector organisations provided a range of social services throughout New Zealand's colonial history. However, it was not until the 1980s that third sector organisations providing comprehensive primary medical and related services started having a significant presence in New Zealand. In 1994 a range of union health centres, tribally based Mäori health providers, and community-based primary care providers established a formal network -- Health Care Aotearoa. While not representing all third sector primary care providers in New Zealand, Health Care Aotearoa was the best-developed example of a grouping of third sector primary care organisations. Member organisations served populations that were largely non-European and lived in deprived areas, and tended to adopt population approaches to funding and provision of services. The development of Health Care Aotearoa has been consistent with international experience of third sector involvement -- there were perceived "failures" in government policies for funding primary care and private sector responses to these policies, resulting in lack of universal funding and provision of primary care and continuing patient co-payments. The principal policy implication concerns the role of the third sector in providing primary care services for vulnerable populations as a partial alternative to universal funding and provision of primary care. Such an alternative may be convenient for proponents of reduced state involvement in funding and provision of health care, but may not be desirable from the point of view of equity and social cohesion insofar as the role of the welfare state is diminished.