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-tank funding often includes a combination of donations from very wealthy people and those not so wealthy, 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.

This article lists global policy institutes according to continental categories and then sub-categories by country within those areas. These listings are not comprehensive; there are at least 11,175 think tanks around the world.