Open Society Foundations ( OSF ), formerly the Open Society Institute , is an international grantmaking network founded by business magnate George Soros.  Open Society Foundations financially support civil society groups around the world, with a stated aim of advancing justice, education, public health and independent media. 
The OSF has branches in 37 countries,  encompassing a group of country and regional foundations, such as the Open Society Initiative for West Africa, and the Open Society Initiative for Southern Africa ; its headquarters are in New York, New York.
On May 28, 1984, Soros signed a contract between the Soros Foundation (New York) and the Hungarian Academy of Sciences, the founding document of the Soros Foundation Budapest.  This was followed by several foundations in the region to help countries move away from communism.
In 1991 the foundation merged with the Fondation pour une Entraide Intellectuelle Européenne, an affiliate of the Congress for Cultural Freedom, created in 1966 to imbue 'non-conformist' Eastern European scientists with anti-totalitarian and capitalist ideas. 
In August 2010, it started using the name of Open Society Foundations (OSF) to better reflect its role as a funder for civil society groups around the world. 
In 2012, Christopher Stone joined the OSF as the second president. He replaced Aryeh Neier, who served as president from 1993 to 2012.  Stone announced in September 2017 that he was stepping down as president. 
In 2016, the OSF was reportedly the target of a cyber security breach. Documents and information reportedly belonging to the OSF were published by a Web site. The cyber security breach has been described as sharing similarities with Russian-linked cyberattacks that targeted other institutions, such as the Democratic National Committee. 
In 2017, Soros transferred $18 billion to the Foundation. 
The Open Society Foundations reported annual expenditures of $827 million in 2014.  Its $873 million budget in 2013, ranked as the second largest private philanthropy budget in the United States, after the Bill and Melinda Gates Foundation budget of $3.9 billion. 
According to the foundations' website, 1993-2014 expenditures included: 
- $2.9 billion to defend human rights, especially the rights of women ; ethnic, racial, and religious minorities ; drug users ; sex workers ; and LGBTQ communities ;
- $2.1 billion for education;
- $1.6 billion on developing democracy in Eastern Europe and the former Soviet Union ;
- $1.5 billion in the United States to promote reform in criminal justice, drug policy, palliative care, education, immigration, equal rights, and democratic governance ;
- $737 million for public health issues such as HIV and AIDS, TB, palliative care, harm reduction, and patients' rights ;
- $214 million to advance the rights of Roma communities in Europe.
Expenditures in 2014 included: 
- $277.3 million - Rights and Justice
- $238.0 million - Governance and Accountability
- $116.0 million - Administration
- $91.7 million - Education and Youth
- $60.0 million - Health
- $43.8 million - Media and Information.
Within these totals, OSF reported granting at least $33 million to civil rights and social justice organizations in the United States.  This funding included groups such as the Organization for Black Struggle and Missourians Organizing for Reform and Empowerment that supported protests in the wake of the shooting of Trayvon Martin, the death of Eric Garner, the shooting of Tamir Rice and the shooting of Michael Brown.    According to the Center for Responsive Politics, the OSF spends much of its resources on democratic causes around the world, and has also contributed to groups such as the Tides Foundation. 
OSF projects have included the National Security and Human Rights Campaign and the Lindesmith Center, which conducted research on drug reform.
In 2007, Nicolas Guilhot (a senior research associate of CNRS) wrote in Critical Sociology that the Open Society Foundations serve to perpetuate institutions which reinforce the existing social order, as the Ford Foundation and Rockefeller Foundation have done before them. Guilhot argues that control over the social sciences by monied interests has depoliticized this field and reinforced a capitalist view of modernization. 
An OSF effort in 2008 in the African Great Lakes region aimed at spreading human rights awareness among prostitutes in Uganda and other nations in the area was not received well by the Ugandan authorities, who considered it an effort to legalize and legitimize prostitution. 
Open Society Foundation has been criticized in pro-Israel editorials, Tablet Magazine, Arutz Sheva and Jewish Press, for including funding for the activist groups Adalah and I'lam, which they say are anti-Israel and support the Boycott, Divestment and Sanctions. Among the documents released by DCleaks, an OSF report reads "For a variety of reasons, we wanted to construct a diversified portfolio of grants dealing with Israel and Palestine, funding both Israeli Jewish and PCI (Palestinian Citizens of Israel) groups as well as building a portfolio of Palestinian grants and in all cases to maintain a low profile and relative distance—particularly on the advocacy front."    NGO monitor, an Israeli NGO, produced a report which says, "Soros has been a frequent critic of Israeli government policy, and does not consider himself a Zionist, but there is no evidence that he or his family holds any special hostility or opposition to the existence of the state of Israel. This report will show that their support, and that of the Open Society Foundation, has nevertheless gone to organizations with such agendas." The report says its objective is to inform OSF, claiming: "The evidence demonstrates that Open Society funding contributes significantly to anti-Israel campaigns in three important respects: 1. Active in the 'Durban strategy;' 2. Funding aimed at weakening U.S.support for Israel by shifting public opinion regarding the Israeli-Palestinian conflict and Iran; 3. Funding for Israeli political opposition groups on the fringes of Israeli society, which use the rhetoric of human rights to advocate for marginal political goals." The report concludes, "Yet, to what degree Soros, his family, and the Open Society Foundation are aware of the cumulative impact on Israel and of the political warfare conducted by many of their beneficiaries is an open question." 
Several politicians in eastern Europe, including Liviu Dragnea in Romania and typically right-wing figures Szilard Nemeth in Hungary, FYROM ’s Nikola Gruevski, who called for a "de-Sorosization" of society, and Poland ’s Jaroslaw Kaczynski, who has said that Soros-funded groups want "societies without identity", regard many of the NGO groups to be irritants at best, and threats at worst.  Some of those Soros-funded advocacy groups in the region say the renewed attacks are harassment and intimidation, which became more open after the election of Donald Trump in the United States. Stefania Kapronczay of the Hungarian Civil Liberties Union, which receives half of its funding from Soros-backed foundations, claims that Hungarian officials are "testing the waters" in an effort to see "what they can get away with."