GiveWell is an American charity evaluator. GiveWell was founded in 2007 by Holden Karnofsky and Elie Hassenfeld, who aimed to rigorously assess the effectiveness of non-profits with the techniques they used while working at a hedge fund. They received early funding from the William and Flora Hewlett Foundation's Nonprofit Marketplace Initiative. GiveWell later partnered with Good Ventures to establish Open Philanthropy.