Leonard P. Liggio is a libertarian Professor of Law at George Mason University, Executive Vice President of the Atlas Economic Research Foundation, and President of the Mont Pelerin Society (2002-2004).
As part of the circle of stateless capitalists led by Murray N. Rothbard during the 1950s, he played an important role in the development of libertarian capitalist philosophy in America.
In 1958, Leonard Liggio attended the first meeting of the Mont Pelerin Society in America, held at Princeton University.
In 1965, Rothbard, Liggio and George Resch created Left and Right, Inc., in New York City, an organization which emphasized the "common philosophical bonds uniting the anarchism and isolationism of the Old Right, and the instinctive pacifistic anarchism characterizing the New Left in the middle sixties." The journal went on to become the "Libertarian Forum" in 1969. 
Liggio serves on the boards of a large number of libertarian think-tanks, almost all of which are supported by the Atlas Foundation.
"In Europe, however, the think tank movement has become stagnant. Its business community appears to have forgotten the secret uncovered by Antony Fisher: think tanks can be the most effective, yet subtle, vehicles for influencing the development of public policy and the deliberations of governments." 
- Atlas Economic Research Foundation, executive vice president
- Mont Pelerin Society, President
- Competitive Enterprise Institute, Director
- Institute for Economic Studies (Europe), Board Member
- Virginia Institute for Public Policy, Board Member
- Foundation for Individual Rights in Education, Board Member
- Institute for Humane Studies, Distinguished Senior Scholar
- Philadelphia Society, trustee, former President
- Freedom Project (John Templeton Foundation), Executive Director
- George Mason University School of Law, Research Professor
- American Journal of Jurisprudence, editorial board
- Markets & Morality, editorial board
- Cato Journal, editorial board
- Howard Center for Family, Religion, and Society, advisory board
- the Fund for American Studies, advisory board
- Academic Council, Fund for American Studies
- Social Affairs Unit, advisory board
- Social Change Project, advisory board
- International Centre for Economic Research, scientific board
- Acton Institute, former board member
- Center for Education and Research in Free Enterprise, former board member
- Hayek Society, honorary member
- Circle of Tradition and Progress, Steering Committee