Liggio had an international influence. In 1958, he attended his first meeting of the
Mont Pelerin Society in the United States, held at
Princeton University. He became a member of the program committee for the society's 1994 meeting at
Cannes in 1992. In 1996, he became its treasurer until 2000 as well as a member of its Program and Planning Committee for the 1998 Society meeting in Washington, D.C., and of its board of directors until 2006. He became the chairman of its program committee for the 2002 meeting in
London, England. He was then vice-president of the Mont Pelerin Society from 2000 to 2002 and its president from 2002 to 2004. He has been senior vice-president since 2004 and due to leave in 2006. Liggio was a trustee with the
Competitive Enterprise Institute since 1994 and the Institute for Economic Studies-Europe in Aix-en-Provence since 1999. From 1988 to 1998, he had been a trustee of the
Philadelphia Society, of which he was president from 1992 to 1993 and from 1994 to 1995. He had been also a trustee with the Institute for Humane Studies-Europe in Paris from 1989 to 1999 and of the Acton Institute for the Study of Religion and Liberty from 1990 to 1999. He also served on the boards of a number of other think tanks: :Member of the international advisory council, The Social Affairs Unit, Morley House, London, since 1994; :Member, board of trustees, Liberty Fund; :Member, advisory council, Acton Institute, Rome, Italy; Spain; :Member, editorial board, Centro Interdisciplinar de Ética e Economia Personalista, Brazil. As part of the circle of anti-state libertarians led by
Murray Rothbard during the 1950s, he played an important role in the development of
modern libertarian philosophy in the United States. He was also a member of the
Philadelphia Society. == Editorial activities ==