Open Philanthropy is a research and grantmaking foundation that makes grants based on the principles of effective altruism. It was founded as a partnership between GiveWell and Good Ventures. Its current chief executive officer is Alexander Berger, and its main funders are Cari Tuna and Dustin Moskovitz. Moskovitz says that their wealth, worth $16 billion, "belongs to the world. We intend not to have much when we die."

Dustin Moskovitz co-founded Facebook and later Asana, becoming a billionaire in the process. He and Tuna, his wife, were inspired by Peter Singer's The Life You Can Save, and became the youngest couple to sign Bill Gates and Warren Buffett’s Giving Pledge, promising to give away most of their money. Tuna left her journalist position at The Wall Street Journal to focus on philanthropy full-time, and the couple started the Good Ventures foundation in 2011. The organization partnered with GiveWell, a charity evaluator founded by Holden Karnofsky and Elie Hassenfeld. The partnership named itself the "Open Philanthropy Project" in 2014, and began operating independently in 2017. Good Ventures holds the funds and distributes them according to recommendations by Open Philanthropy. As of 2024, Open Philanthropy has made $3.2 billion in public grants through that process.

Open Philanthropy's grantmaking is based on the principles of effective altruism. The organization makes grants across a variety of focus areas, with the goal of “help[ing] others as much as [it] can”. They calculate impact for some programs using back-of-the-envelope calculations, and decide which opportunities to fund using a “bar” for cost-effectiveness. At the same time, they consider their work "high-risk philanthropy", and expect "that most of [their] work will fail to have an impact". In 2023, Open Philanthropy recommended more than $750 million in grants.

Open Philanthropy’s focus areas are split across two portfolios: Global Health and Wellbeing and Global Catastrophic Risks. A few areas fall outside these portfolios.

The Global Health and Wellbeing portfolio includes areas focused on global health, scientific research, farm animal welfare, land use reform, and public policy. Within the portfolio, Open Philanthropy prioritizes causes by evaluating how impactful, neglected, and tractable they seem, while also aiming to equalize marginal returns across different interventions to maximize overall impact.

Historically, a large fraction of funding in this portfolio went toward charities recommended by GiveWell. More recently, Open Philanthropy has pushed to identify causes that could leverage funding to “get more humanitarian impact per dollar”, leading to the creation of several new programs (in areas such as public health and innovation policy) and leaving GiveWell as a smaller portion of the portfolio.

Open Philanthropy's investments in global health and development include efforts to cure iodine deficiencies, prevent malaria, and scale up vaccine production. Of their global health and development giving, Tuna said, “I am still optimistic that we can do better than just giving money to poor people, but in the meantime, we’re doing a lot of just giving money to poor people.”

Holden Karnofsky has claimed that Open Philanthropy "is the largest funder in the world of farm animal welfare", including investing in alternative proteins and animal welfare advocacy. In 2016, Open Philanthropy made an investment in Impossible Foods to support the development of non-animal meats. It is also a patron of The Good Food Institute. Research done by Open Philanthropy includes an investigation of the economic viability of cultivated meat.

Grants within the science bucket include the areas of human health and wellbeing, scientific innovation, science supporting biosecurity and pandemic preparedness, transformative basic science, and other scientific research areas. As of April 2024, Open Philanthropy has funded more than $320 million in science-focused grants.

Grants in this portfolio include:

• Over $250 million to Malaria Consortium, for seasonal malaria chemoprevention programs in countries including Nigeria, Burkina Faso, Chad, Togo, and Mozambique.
• Over $48 million (and up to $64.7 million) to Evidence Action to support the Dispensers for Safe Water program, which installs free chlorine dispensers near water sources to improve water safety and avert deaths from diarrheal diseases.
• Over $47 million to GiveDirectly, partially for research to compare the effectiveness of giving money with more traditional developmental aid, and including at least $16 million to be given directly to people in extreme poverty in Kenya and Uganda.
• Over $40 million to The Humane League, to advocate for better conditions for egg-laying hens and broiler chickens.
• $17.5 million to Sherlock Biosciences, for viral diagnostic tools.
• $2.4 million to the Center for Election Science.
• $500,000 to California YIMBY. Open Philanthropy was the first institutional funder of the YIMBY movement.
• $150,000 to the Lead Exposure Elimination Project, for general support

Under this portfolio, Open Philanthropy supports organizations aimed at tackling global catastrophic risks. This category includes over $200 million given for biosecurity and pandemic preparedness, and over $370 million for mitigating potential risks from advanced artificial intelligence. The organization tends to prioritize interventions aimed at reducing risks with the potential to "kill enough people to threaten civilization as we know it", because preventing such risks is expected to save the most lives. Some have claimed that by "flooding" money into biosecurity, Open Philanthropy is "absorbing much of the field’s experienced research capacity, focusing the attention of experts on this narrow, extremely unlikely, aspect of biosecurity risk". On the 80,000 Hours podcast, whose largest funder is Open Philanthropy, some biosecurity experts, however, have anonymously counseled against "failures of imagination", overreliance on historical precedents, and other ways of thinking that could lead people to underestimate catastrophic biorisk.

Grants in this portfolio include:

• About $38 million to the Johns Hopkins Center for Health Security.
• $11.3 million to the University of Washington’s Institute for Protein Design to develop a universal flu vaccine.
• About $23 million to the Effective Ventures Foundation (EVF) for the purchase of Wytham Abbey as a venue for hosting conferences and other events related to global catastrophic risk. In 2024, Open Philanthropy announced that after evaluating the cost-effectiveness of the space, they asked EVF to sell it, and that proceeds from the sale will be distributed to other EVF projects.
• $55 million to create the Center for Security and Emerging Technology.
• $5.5 million to launch the Center for Human-Compatible Artificial Intelligence at UC Berkeley.

Past focus areas of Open Philanthropy have included criminal justice reform (which spun out as a new organization in 2021) and US macroeconomic stabilization policy (which ceased to be a focus in 2021, though European macroeconomic policy grants have been made more recently).

Grants in past focus areas include:

• $50 million to Just Impact Advisors, to advise philanthropists and make grants related to criminal justice.
• $335,000 to the Full Employment Project at the Center for Budget and Policy Priorities.
• $3 million to the Pew Charitable Trusts' Public Safety Performance Project, to “reduce incarceration and correctional spending while maintaining or improving public safety and concentrating prison beds on high level offenders" at the state level.

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