The John D. and Catherine T. MacArthur Foundation is a prominent American private foundation and major U.S. philanthropic organization dedicated to supporting creative and intellectual pursuits through grants and impact investments to non-profit organizations worldwide. Established in 1978 following the death of its founder, John D. MacArthur, the foundation operates with a mission to foster innovation, address global challenges, and promote social justice. It is renowned for its MacArthur Fellows Program, often called the 'Genius Grants,' which awards unrestricted fellowships to individuals demonstrating exceptional creativity in fields such as arts, sciences, and community work; the foundation itself was a recipient of the MacArthur 'Genius' Fellowship in 1982. With an endowment of approximately $9 billion as of 2025, the foundation distributes hundreds of millions of dollars annually, having awarded billions in total since its inception. Its programs span diverse areas including climate solutions, nuclear security, journalism and media, population and reproductive health, and community development, impacting initiatives in about 117 countries. Headquartered in Chicago, Illinois, the MacArthur Foundation ranks among the 20 largest private foundations in the United States. It emphasizes long-term, catalytic investments that encourage bold ideas and systemic change, often partnering with grantees to amplify their efforts. The foundation's approach is guided by a commitment to equity, sustainability, and human rights, with recent focuses on mitigating climate change, strengthening democratic institutions, and supporting independent journalism. While primarily grant-making, it also engages in impact investing to align financial returns with social good. The organization's influence extends through its board of trustees, comprising leaders from various sectors, and its transparent reporting on grant allocations and strategic priorities.