Non-governmental organization (NGO) is a term that has become widely accepted for referring to a legally constituted, non-business organization created by natural or legal persons with no participation or representation of any government. In the cases in which NGOs are funded totally or partially by governments, the NGO maintains its non-governmental status insofar as it excludes government representatives from membership in the organization. Unlike the term intergovernmental organization, "non-governmental organization" is a term in generalized use but not a legal definition, in many jurisdictions these type of organizations are defined as "civil society organizations" or alternative terms.
The number of internationally operating NGOs is estimated at 40,000. National numbers are even higher: Russia has 277,000 NGOs. India is estimated to have between 1 million and 2 million NGOs.
International non-governmental organizations have a history dating back to at least 1914 (Rotary, later Rotary International, was founded in 1904), where there were 1083 NGO's. They were important in the anti-slavery movement and the movement for women's suffrage, and reached a peak at the time of the World Disarmament Conference. However, the phrase "non-governmental organization" only came into popular use with the establishment of the United Nations Organization in 1945 with provisions in Article 71 of Chapter 10 of the United Nations Charter for a consultative role for organizations which are neither governments nor member states—see Consultative Status. The definition of "international NGO" (INGO) is first given in resolution 288 (X) of ECOSOC on February 27, 1950: it is defined as "any international organization that is not founded by an international treaty". The vital role of NGOs and other "major groups" in sustainable development was recognized in Chapter 27 of Agenda 21, leading to intense arrangements for a consultative relationship between the United Nations and non-governmental organizations.
Rapid development of nongovernmental sector occurred in western countries as a result of the processes of restructurization of the welfare state. Further globalisation of that process occurred after a fall of communist system and was important part of Washington consensus  .
Globalization during the 20th century gave rise to the importance of NGOs. Many problems could not be solved within a nation. International treaties and international organizations such as the World Trade Organization were perceived as being too centred on the interests of capitalist enterprises. Some argued that in an attempt to counterbalance this trend, NGOs have developed to emphasize humanitarian issues, developmental aid and sustainable development. A prominent example of this is the World Social Forum which is a rival convention to the World Economic Forum held annually in January in Davos, Switzerland. The fifth World Social Forum in Porto Alegre, Brazil, in January 2005 was attended by representatives from more than 1,000 NGOs. Some have argued that in forums like these, NGOs take the place of what should belong to popular movements of the poor. Others argue that NGOs are often imperialist in nature, that they sometimes operate in a racialized manner in dominated countries, and that they fulfil a similar function to that of the clergy during the high colonial era. The philosopher Peter Hallward argues that they are an aristocratic form of politics.  Whatever the case, NGO transnational networking is now extensive.
Apart from "NGO", often alternative terms are used as for example: independent sector, volunteer sector, civil society, grassroots organizations, transnational social movement organizations, private voluntary organizations, self-help organizations and non-state actors (NSA's).
Non-governmental organizations are a heterogenous group. A long list of acronyms has developed around the term "NGO".
The primary purpose of an operational NGO is the design and implementation of development-related projects. One frequently used categorization is the division into :relief-oriented: or :development-oriented: organizations; they can also be classified according to whether they stress service delivery or participation; or whether they are religious or secular; and whether they are more public or private-oriented. Operational NGOs can be community-based, national or international.
The primary purpose of an Advocacy NGO is to defend or promote a specific cause. As opposed to operational project management, these organizations typically try to raise awareness, acceptance and knowledge by lobbying, press work and activist events.
USAID refers to NGOs as private voluntary organisations. However many scholars have argued that this definition is highly problematic as many NGOs are in fact state and corporate funded and managed projects with professional staff. Furthermore it has often been argued that USAID is in fact a key arm of American imperialism and that it sets up and supports NGOs in order to further imperial agendas. 
NGOs exist for a variety of reasons, usually to further the political or social goals of their members or funders. Examples include improving the state of the natural environment, encouraging the observance of human rights, improving the welfare of the disadvantaged, or representing a corporate agenda. However, there are a huge number of such organizations and their goals cover a broad range of political and philosophical positions. This can also easily be applied to private schools and athletic organizations.
NGOs vary in their methods. Some act primarily as lobbyists, while others conduct programs and activities primarily. For instance, an NGO such as Oxfam, concerned with poverty alleviation, might provide needy people with the equipment and skills to find food and clean drinking water, whereas an NGO like the FFDA helps through investigation and documentation of human rights violations and provides legal assistance to victims of human rights abuses.
Non-governmental organizations need healthy relationships with the public to meet their goals. Foundations and charities use sophisticated public relations campaigns to raise funds and employ standard lobbying techniques with governments. Interest groups may be of political importance because of their ability to influence social and political outcomes.
Many international NGOs have a consultative status with United Nations agencies relevant to their area of work. As an example, the Third World Network has a consultative status with the UN Conference on Trade and Development (UNCTAD) and the UN Economic and Social Council (ECOSOC). While in 1946, only 41 NGOs had consultative status with the ECOSOC, by 2003 this number had risen to 3,550.
There is an increasing awareness that management techniques are crucial to project success in non-governmental organizations. Generally, non-governmental organizations that are private have either a community or environmental focus. They address varieties of issues such as religion, emergency aid, or humanitarian affairs. They mobilize public support and voluntary contributions for aid; they often have strong links with community groups in developing countries, and they often work in areas where government-to-government aid is not possible. NGOs are accepted as a part of the international relations landscape, and while they influence national and multilateral policy-making, increasingly they are more directly involved in local action.
Not all people working for non-governmental organizations are volunteers. The reasons people volunteer are not necessarily purely altruistic, and can provide immediate benefits for themselves as well as those they serve, including skills, experience, and contacts.
There is some dispute as to whether expatriates should be sent to developing countries. Frequently this type of personnel is employed to satisfy a donor who wants to see the supported project managed by someone from an industrialized country. However, the expertise these employees or volunteers may have can be counterbalanced by a number of factors: the cost of foreigners is typically higher, they have no grassroot connections in the country they are sent to, and local expertise is often undervalued.
The NGO sector is an important employer in terms of numbers. For example, by the end of 1995, CONCERN worldwide, an international Northern NGO working against poverty, employed 174 expatriates and just over 5,000 national staff working in ten developing countries in Africa and Asia, and in Haiti.
Large NGOs may have annual budgets in the hundreds of millions or billions of dollars. For instance, the budget of the American Association of Retired Persons (AARP) was over US$540 million in 1999. . Funding such large budgets demands significant fundraising efforts on the part of most NGOs. Major sources of NGO funding include membership dues, the sale of goods and services, grants from international institutions or national governments, and private donations. Several EU-grants provide funds accessible to NGOs.
Even though the term "non-governmental organization" implies independence from governments, most NGOs depend heavily on governments for their funding . A quarter of the US$162 million income in 1998 of the famine-relief organization Oxfam was donated by the British government and the EU. The Christian relief and development organization World Vision collected US$55 million worth of goods in 1998 from the American government. Nobel Prize winner Médecins Sans Frontières (MSF) (known in the USA as Doctors Without Borders) gets 46% of its income from government sources.
In a March 2000 report on United Nations Reform priorities, former U.N. Secretary General Kofi Annan wrote in favor of international humanitarian intervention, arguing that the international community has a "right to protect" citizens of the world against ethnic cleansing, genocide, and crimes against humanity. On the heels of the report, the Canadian government launched the Responsibility to Protect project, outlining the issue of humanitarian intervention. While the R2P doctrine has wide applications, among the more controversial has been the Canadian government's use of R2P to justify its intervention and support of the coup in Haiti.
Years after R2P, the World Federalist Movement, an organization which supports "the creation of democratic global structures accountable to the citizens of the world and call for the division of international authority among separate agencies", has launched Responsibility to Protect - Engaging Civil Society (R2PCS). A collaboration between the WFM and the Canadian government, this project aims to bring NGOs into lockstep with the principles outlined under the original R2P project.
The governments of the countries an NGO works or is registered in may require reporting or other monitoring and oversight. Funders generally require reporting and assessment, such information is not necessarily publicly available. There may also be associations and watchdog organizations that research and publish details on the actions of NGOs working in particular geographic or program areas.
In recent years, many large corporations have increased their corporate social responsibility departments in an attempt to preempt NGO campaigns against certain corporate practices. As the logic goes, if corporations work with NGOs, NGOs will not work against corporations.
In December 2007, The United States Department of Defense Assistant Secretary of Defense (Health Affairs) http://en.wikipedia.org/wiki/S._Ward_Casscells established an International Health Division under Force Health Protection & Readiness http://www.ha.osd.mil/FHPR/default.cfm. Part of International Health's mission is to communicate with NGOs in areas of mutual interest. Department of Defense Directive 3000.05 http://www.dtic.mil/whs/directives/corres/pdf/300005p.pdf, in 2005, requires DoD to regard stability-enhancing activities as a mission of importance equal to warfighting. In compliance with international law, DoD has necessarily built a capacity to improve essential services in areas of conflict such as Iraq, where the customary lead agencies (State Department and USAID) find it difficult to operate. Unlike the "co-option" strategy described for corporations, the OASD(HA) recognizes the neutrality of health as an essential service. International Health cultivates collaborative relationships with NGOs, albeit at arms-length, recognizing their traditional independence, expertise and honest broker status. While the goals of DoD and NGOs may seem incongruent, the DoD's emphasis on stability and security to reduce and prevent conflict suggests, on careful analysis, important mutual interests.
NGOs are not subjects of international law, as states are. An exception is the International Committee of the Red Cross, which is subject to certain specific matters, mainly relating to the Geneva Convention.
The Council of Europe in Strasbourg drafted the European Convention on the Recognition of the Legal Personality of International Non-Governmental Organizations in 1986, which sets a common legal basis for the existence and work of NGOs in Europe. Article 11 of the European Convention on Human Rights protects the right to freedom of association, which is also a fundamental norm for NGOs.
There is a growing movement within the “non”-profit and “non”-government sector to define itself in a more constructive, accurate way. Instead of being defined by “non” words, organizations are suggesting new terminology to describe the sector. The term “civil society organization” (CSO) has been used by a growing number of organizations, such as the Center for the Study of Global Governance.  The term “citizen sector organization” (CSO) has also been advocated to describe the sector — as one of citizens, for citizens. This labels and positions the sector as its own entity, without relying on language used for the government or business sectors. However some have argued that this is not particularly helpful given that most NGOs are in fact funded by governments and business and that some NGOs are clearly hostile to independently organized people's organizations. 
More useful are regional histories and analyses of the experience of NGOs. Specific works (although this is by no means an exhaustive list) include:
The de facto reference resource for information and statistics on International NGOs (INGOs) and other transnational organisational forms is the Yearbook of International Organizations, produced by the Union of International Associations.
Glasius, Marlies, Mary Kaldor and Helmut Anheier (eds.) "Global Civil Society 2006/7". London: Sage, 2005.