Evidence Action is an American non-profit organization founded in 2013 that scales cost-effective development interventions with rigorous evidence supporting their efficacy. The organization operates four main programs: the Deworm the World Initiative, Safe Water Now, Equal Vitamin Access, and Syphilis-Free Start. It also operates an Accelerator program, whereby new development interventions are screened and scaled according to efficacy. Vox Media has described Evidence Action as taking a "VC approach to development work".

Evidence Action has frequently been ranked as among the most effective charities in the world, scaling programs in global health whose cost effectiveness is supported by randomized controlled trials. The charity is guided by principles of effective altruism, in particular the notion that charitable giving should be oriented towards the causes that do the most good in the world. In 2022, the organization's revenue was US$127 million.

Evidence Action was founded in 2013 as the parent organization for the Deworm the World Initiative, an international deworming campaign co-founded by economists Kristin Forbes, Michael Kremer, Esther Duflo, and Rachel Glennerster. In 2004, Kremer and co-author Edward Miguel published an impact evaluation of a school-based deworming campaign in Kenya, showing that the program increased school attendance rates by 25% and improved overall health. Kremer and Esther Duflo presented the findings of this and other research at the World Economic Forum in 2007, founding the Deworm the World Initiative as an independent organization to scale school-based deworming schemes. From 2010 to 2014, Deworm the World was incubated by Innovations for Poverty Action, a non-profit research and policy organization advocating the use of rigorous impact evaluation in international development.

In 2013, Evidence Action was founded to manage Deworm the World. Alix Zwane, Evidence Action's first executive director, articulated the organization's mandate as being based on the "gap between what research shows is effective in global development and what is implemented in practice." The organization is now run by Kanika Bahl, a former Executive Vice President of the Clinton Health Access Initiative. From 2013 to 2022, Evidence Action was ranked a top-rated charity by GiveWell, considered among the best internationally for social impact per dollar spent.

Many businesspeople, journalists, and prominent figures in the effective altruism movement have donated to or advocated for donating to Evidence Action, including Peter Singer, Ezra Klein, Nicholas Kristof, Dylan Matthews, Dustin Moskovitz, and Cari Tuna.

Evidence Action operates four distinct programs: Deworm the World, Safe Water Now, Equal Vitamin Access, and Syphilis-Free Start. The first two of these were incubated by Innovations for Poverty Action, and are implemented at-scale. The latter two were launched via Evidence Action's Accelerator program, whereby promising interventions are piloted and scaled conditional on performance.

Evidence Action's flagship program is Deworm the World, a school-based deworming scheme active in Kenya, India, Ethiopia, Nigeria, and Vietnam. The Deworm the World Initiative was founded in 2007, in response to an experimental evaluation of a school-based deworming campaign in Busia, Kenya. After completing an undergraduate degree at Harvard University, Michael Kremer worked for a year as a teacher in the Kakamega District of Kenya. He returned to the area with Rachel Glennerster, his wife, after completing his PhD, and learned of a local friend's plan to implement a deworming program in nearby schools. Interested in the effects of the program, he organized a randomized controlled trial, rolling out treatments in 1998. In 2004, Kremer and Edward Miguel, his PhD student, published the results of the evaluation in Econometrica.

The results of the study indicated that deworming is a cost effective means of improving health and education outcomes, raising school attendance rates by 25%. The study's treatment effects suggested that for each $100 spent on deworming, students would collectively gain another 13.9 years of schooling. Results from the experiment were presented by Kremer and Esther Duflo at the World Economic Forum in 2007, inspiring the creation of the Deworm the World Initiative, an international deworming campaign incubated by Innovations for Poverty Action. In 2009, Deworm the World began working with the Kenyan government to train teachers and other school employees to administer oral deworming treatments to students. In 2012, a full-scale roll-out was launched, with treatments administered in a series of "deworming days" across the country. A similar campaign was launched in India, where Deworm the World supported preliminary surveys of the worm burdens across various Indian states and helped rolled-out treatment to over 17 million children in the state of Bihar. In 2013, Evidence Action was founded to manage and scale the Deworm the World Initiative.