This dissertation presents the political proposal of Karl Popper, from its origins in his epistemological proposal to his defense of his fundamental political bet: an open society. A proposal and defense of a society that establishes relationships based on reason, and on a model of scientific discussion and progress II is not about bringing heaven to earth. It s about proposing an open society, and more than that, it has to deal with defending the bases upon which nowadays open societies and democracies have been constructed. Karl Popper's critics of utopianism, and of course the notion of truth in positivism, binds together with a fundamental agreement on what science and a good society must be. Popper' proposals on science and society are done from reason itself, but not an isolated reason, but a rationality product of a community and its interactions.