The Adam Smith Institute (ASI) is a neoliberal (formerly libertarian) think tank and lobbying group based in the United Kingdom and named after Adam Smith, a Scottish moral philosopher and classical economist. The libertarian label was officially changed to neoliberal on 10 October 2016. The Institute advocates free market and classical liberal ideas, primarily via the formation of policy options with regard to public choice theory, which political decision makers seek to develop upon. ASI President Madsen Pirie has sought to describe the activity of the organisation as "[w]e propose things which people regard as being on the edge of lunacy. The next thing you know, they're on the edge of policy".

The ASI formed the primary intellectual force behind privatisation of state-owned industries during the premiership of Margaret Thatcher and alongside the Centre for Policy Studies and Institute of Economic Affairs advanced a neoliberal approach toward public policy on privatisation, taxation, education and healthcare. A number of the policies presented by organisation were adopted by the administrations of John Major and Tony Blair and members of the ASI have also advised non-United Kingdom governments.

Beyond policy development, the organisation advocates free market ideas through the publication and distribution of literature, the promotion of Tax Freedom Day, the hosting of speaker events for students and young people, media appearances and blogging.