The Acton Institute for the Study of Religion and Liberty is an American conservative and libertarian think tank in Grand Rapids, Michigan, with an office in Rome. Its stated mission is "to promote a free and virtuous society characterized by individual liberty and sustained by religious principles". Its work supports free market economic policy framed within Judeo-Christian morality. Acton Institute also organizes seminars "to educate religious leaders of all denominations, business executives, entrepreneurs, university professors, and academic researchers in economics principles".

The Acton Institute was founded in 1990 in Grand Rapids, Michigan by Robert A. Sirico and Kris Alan Mauren. It is named after the English historian, politician and writer Lord Acton, who is popularly associated with the dictum "Power tends to corrupt, and absolute power corrupts absolutely". The institute is a member of the Atlas Network.

Sirico and Mauren were concerned that many religious people were ignorant of economic realities, and that many economists and businessmen were insufficiently grounded in religious principles. Sirico explained the link between economics and religion with reference to the institute's namesake: "Acton realized that economic freedom is essential to creating an environment in which religious freedom can flourish. But he also knew that the market can function only when people behave morally. So, faith and freedom must go hand in hand. As he put it, 'Liberty is the condition which makes it easy for conscience to govern.'"

The release in 1991 of the papal encyclical Centesimus annus buoyed the institute at a critical time. The document provided, a year after Acton's founding, established support for the institute's economic personalism and defense of capitalism. Robert Sirico said at the time that it constituted a "vindication". In 2000, the institute was involved in establishing the Cornwall Alliance for the Stewardship of Creation, described by Deutsche Welle and The New Republic as a climate denial group.

In 2002, the institute opened a Rome office, Istituto Acton, to carry out Acton's mission abroad.

In 2005, Mother Jones published a chart which included the Acton Institute on a list of groups that had received a donation ($155,000) from ExxonMobil. As of 2007, the institute had received funding from the Earhart Foundation and the Bradley Foundation. The Grand Rapids Press wrote in 2013 that much of the Acton Institute's funding comes from wealthy residents of western Michigan, including John Kennedy, president and CEO of Autocam Corp., and Amway co-founder Richard DeVos. The New Republic said in 2023 that the Acton Institute has "long pushed a Christian-flavored brand of climate denial".

The Acton Institute is a member of the State Policy Network, a network of free-market oriented think tanks in the United States. The Acton Institute has built a network of international affiliations including Centro Interdisciplinar de Ética e Economia Personalista, Brazil, Europa Institut, Austria, Institute for the Study of Human Dignity and Economic Freedom, Zambia and Instituto Acton Argentina Organization.

The institute publishes books, papers, and periodicals, and maintains a media outreach effort.