A non-governmental organization (NGO) is an organization that is not formally part of the public sector — either as a department or agency, or any other entity directly under the authority of, or reporting to, the executive, legislative, or judicial branch of government. In principle, this definition would include the private sector, but business organizations are quite different from religious organizations, charitable groups, neighbourhood groups, and the voluntary sector in the way in which they interact with government. NGOs are crucial to modern societies in several ways. They make up most of what we think of as "civil society" — the arena of organized social life that is distinct from the market and from politics. They often are created to represent certain interests or causes — for example, Greenpeace in the environmental arena or Amnesty International on human rights issues. In this sense, while non-governmental, NGOs are usually entangled in the political process, championing one cause or interest or another.
From a political system perspective, the configuration of NGOs makes up a country's "associational system." This refers to the number of NGOs, their organizational capacities, their relationships to each other, and ultimately to the state itself. Some countries have very dense and active associational systems, others ones that are less so. The determining factors appear to be the political culture of "joining," the accessibility of the political system to outside interests, and the independence of civil society from the state.
NGOs increasingly are rooted domestically but act globally. The Yearbook of International Organizations estimates that in 2004 there were some 44,000 international NGOs, up from 7,500 in 1991. Globalization has helped contribute to an increase in NGOs at the local, national, and international levels, and has encouraged more local NGOs to connect to international networks. As political decision-making moves to the global level, so have NGO activities.