The term NGO is very broad and encompasses many different types of organizations. In the field of development, NGOs range from large, Northern-based charities such as CARE, Oxfam and World Vision to community-based self-help groups. They also include research institutes, churches, professional associations and lobby groups The World Bank tends to interact with two main categories of NGOs: Operational NGOs - whose primary purpose is the design and implementation of development-related projects, and; Advocacy NGOs - whose primary purpose is to defend or promote a specific cause and who seek to influence the policies and practices of the World Bank.

In 1992 international NGOs channeled over $7.6 billion of aid to developing countries. It is now estimated that over 15 percent of total overseas development aid is channeled through NGOs. While statistics about global numbers of NGOs are notoriously incomplete, it is currently estimated that there is somewhere between 6,000 and 30,000 national NGOs in developing countries.

Further definition of an NGO

The diversity of NGOs strains any simple definition. They include many groups and institutions that are entirely or largely independent of government and that have primarily humanitarian or cooperative rather than commercial objectives. They are private agencies in industrial countries that support international development; indigenous groups organized regionally or nationally; and member-groups in villages. NGOs include charitable and religious associations that mobilize private funds for development, distribute food and family planning services and promote community organization. They also include independent cooperatives, community associations, water-user societies, women's groups and pastoral associations. Citizen Groups that raise awareness and influence policy are also NGOs.