Estimated to have tens of millions of  followers, some

identifying themselves  as adherent to other ethical systems as well (this dual adherence also

happens for other pairs of ethical systems, which do not include Liberalism), Liberalism may be the

fourth largest ethical system in the world.

About Liberalism

Liberalism is a minimalist man-made ethical system. One may shortly describe a famous and common version of the Liberalism this way (consisting of rules mostly accepted by other mentioned ethical systems - in fact, the mentioned ethical systems have much in common):

http://www.un.org/Overview/rights.html