The article presents the definitions, objectives, fields and tasks of non-governmental organizations in social life, health system and health policy. In addition, the article addresses the issue of effectiveness and quality of NGOs' activity. The term "NGOs" (Non-governmental Organizations) includes different categories of entities that operate not to obtain financial gain, and also do not belong to the government sector. Non-governmental Organizations' fields of activity were described in the International Classification of Non-Profit Organizations (ICNPO). NGOs are an integral part of a democratic society. Sociological sciences emphasize their importance in enhancing social integration, implementation of the principle of subsidiarity, building civil society, social dialogue and participatory democracy. The main tasks of NGOs in the health system are providing services and health advocacy. Provision of services includes medical, social and psychological services as well as, integration activities, care and nursing, material and financial support, educational and information services and training. Health advocacy is a combination of individual and social actions designed to gain political commitment, policy support, social acceptance and systems support for a particular health goal or program. An important task carried out by NGOs is participation in the formation of health policy. The increasing role of NGOs in providing social services and the participation in political processes, result in the need to confirm the validity and credibility of their operation. One of the ways could be to introduce the mechanisms to assess quality and efficiency, such as registration as a part of a legal system, self-regulatory activities (card rules, codes of ethics), certification, participation in networks, monitoring and audit.