Global Witness is an international NGO which investigates environmental and human rights abuses.

The organisation, which has offices in London, Washington, D.C. and Brussels, explores how diamonds and other natural resources can fund conflict or fuel corruption. It carries out investigations into the involvement of specific individuals and business entities in activities such as illegal and unsustainable forest exploitation, and corruption in oil, gas and mining industries, and campaigns for greater representation of people affected by the climate crisis in climate decision-making.

Global Witness has worked on diamonds, oil, timber, cocoa, gas, gold and other minerals. It has undertaken investigations and case studies in Cambodia, Angola, Liberia, Democratic Republic of the Congo, Equatorial Guinea, Kazakhstan, Burma, Indonesia, Zimbabwe, Turkmenistan and Ivory Coast. It has also helped to set up international initiatives such as the Extractive Industries Transparency Initiative, the Kimberley Process, and the Publish What You Pay coalition.

The organisation campaigns to protect human rights defenders targeted because of their work to prevent natural resource exploitation. An investigation by Global Witness in April 2014 revealed there were nearly three times as many environmental defenders killed in 2012 than 10 years previously. Global Witness documented 147 deaths in 2012, compared to 51 in 2002. In Brazil, 448 activists defending natural resources were killed between 2002 and 2013, in Honduras 109, Peru 58, the Philippines 67, and Thailand 16. Many of those facing threats are ordinary people opposing land grabs, mining operations and the industrial timber trade, often forced from their homes and severely threatened by environmental devastation. Others have been killed for protests over hydroelectric dams, pollution and wildlife conservation. By 2019, Global Witness were documenting 212 such deaths in the year.

Global Witness's first campaign was in Cambodia in the 1990s where the Khmer Rouge was smuggling timber into Thailand. The Observer newspaper attributed the cessation to Global Witness's "detailed and accurate reporting".

After a report implicating relatives of Prime Minister Hun Sen and other senior government officials, the prime minister's brother, Hun Neng, a provincial governor, was quoted in a Cambodian newspaper as saying if anyone from Global Witness returned to Cambodia, he would "hit them until their heads are broken."

As part of its campaign against conflict diamonds, Global Witness helped establish the Kimberley Process Certification Scheme (KCPS). The international governmental certification scheme was set up to stop to trade in blood diamonds, requiring governments to certify that shipments of rough diamonds are conflict-free. Like many other Sub-Saharan African (SSA) countries, Sierra Leone is endowed with oil and mineral resources amid social inequality, high prevalence of poverty, and conflict.

On 19 July 2000, the World Diamond Congress adopted at Antwerp a resolution to reinforce the diamond industry's ability to block sales of conflict diamonds. Thereafter, with growing international pressure from Global Witness and other NGOs, meetings were hosted with diamond-producing countries over three years, concluding in the establishment of an international diamond certification scheme in January 2003. The certification system on the export and import of diamonds, known as the KCPS, was called by the resolution, imposing legislation in all countries to accept shipment of only officially sealed packages of diamonds accompanied by a KP certificate guaranteeing that they were conflict-free. Anyone found trafficking conflict diamonds will be indicted of criminal charges, while bans were to be imposed on individuals found trading those stones from diamond bourses under the World Federation of Diamond Bourses.