International directory of think tanks.
The NGO Branch of the United Nations Department of Economic and Social Affairs (UNDESA) administers the database of NGOs in Consultative Status with ECOSOC.
UNESCO's international directory of NGOs. Includes a map feature.
The World Association of Non-Governmental Organizations is a global organization whose mission is to serve its member organizations, strengthen and encourage the non-governmental sector as a whole, increase public understanding of the non-governmental community, and provide the mechanism and support needed for NGOs to connect, partner, and multiply their contributions to solve humanity's basic problems.