Ideologically, Judge Posner is a
pragmatist, and often uses economic analysis on the interpretation of law. His judicial philosophy was influenced by
Oliver Wendell Holmes, Jr. and
Learned Hand.
Some of Posner's views are regarded as controversial. For example, he believes that in a free market system selling and buying babies are more efficient than the current regime of government-controlled adoption. He also opposes government regulation of business monopolies, and argued that natural monopoly is beneficial for the economy.
Posner opposes the War on Drugs, arguing that criminalizing consensual behavior is economically inefficient, and that it is arbitrary for the government to make some drugs illegal while more dangerous ones (like alcohol and cigarettes) legitimate. However, he also stated that as a sworn judge he would still enforce current laws on drug cases.
Sources:
http://www.theregister.co.uk/1999/11/22/who_the_heck_is_judge/
http://www.ndsn.org/nov95/posner.html
http://www.becker-posner-blog.com/archives/2005/03/the_war_on_drug.html
Posner, Richard 1987. "Adoption and Market Theory: The Regulation of the Market in Adoption" BOSTON UNIVERSITY LAW REVIEW 67: 59-72.