A think tank, or policy institute, is a research institute that performs research and advocacy concerning topics such as social policy, political strategy, economics, military, technology, and culture. Most think tanks are non-governmental organizations, but some are semi-autonomous agencies within government or are associated with particular political parties, businesses or the military. Think-tanks are often funded by individual donations, with many also accepting government grants.

Think tanks publish articles and studies, and even draft legislation on particular matters of policy or society. This information is then used by governments, businesses, media organizations, social movements or other interest groups. Think tanks range from those associated with highly academic or scholarly activities to those that are overtly ideological and pushing for particular policies, with a wide range among them in terms of the quality of their research. Later generations of think tanks have tended to be more ideologically oriented. Modern think tanks began as a phenomenon in the United Kingdom in the 19th and early 20th centuries, with most of the rest being established in other English-speaking countries. Prior to 1945, they tended to focus on the economic issues associated with industrialization and urbanization. During the Cold War, many more American and other Western think tanks were established, which often guided government Cold War policy.  Since 1991, more think tanks have been established in non-Western parts of the world. More than half of all think tanks that exist today were established after 1980.

The American Enterprise Institute for Public Policy Research, known simply as the American Enterprise Institute (AEI), is a center-right think tank based in Washington, D.C., that researches government, politics, economics, and social welfare. AEI is an independent nonprofit organization supported primarily by contributions from foundations, corporations, and individuals. Founded in 1938, the organization is aligned with conservatism and neoconservatism but does not support political candidates. AEI advocates in favor of private enterprise, limited government, and democratic capitalism.

AEI is governed by a 28-member Board of Trustees, composed of executives and former executives from various corporations. Approximately 185 authors are associated with AEI. Arthur C. Brooks served as president of AEI from January 2009 through July 1, 2019. He was succeeded by Robert Doar.

The Brookings Institution, often stylized as Brookings, is an American think tank that conducts research and education in the social sciences, primarily in economics (and tax policy), metropolitan policy, governance, foreign policy, global economy, and economic development.

Brookings has five research programs: Economic Studies, Foreign Policy, Governance Studies, Global Economy and Development, and Metropolitan Policy. It also operated three international centers in Doha, Qatar (Brookings Doha Center); Beijing, China (Brookings-Tsinghua Center for Public Policy); and New Delhi, India (Brookings India) In 2020 and 2021, the Institution announced it was separating entirely from its centers in Doha and New Delhi, and transitioning its center in Beijing to an informal partnership with Tsinghua University, known as Brookings-Tsinghua China.