Karl Raymund Popper comes to liberalism in a mature phase of his philosophical training. Presented as an epistemologist and philosopher of science, the Austrian thinker elaborates a new methodology, based on the criterion of falsifiability of scientific theories and on the progress of science through trial and error. This methodology is actually exported to the political field, proposing a liberal reformist vision in opposition to the a priori planning holism of totalitarian ideologies. Supporting reformism means thinking of an open society; moving in the holistic-totalitarian logic means to outline a closed society. In the Popperian perspective, the approach to the problem of leadership must change: one should not ask “who should govern”, but how to control the rulers and be able to remove them. Popper focuses all his reflection on the role of the individual and in this perspective it is important that even today a political philosophy that privileges the individual over the collective is taken into account, placing, once again, the dimension of individual responsibility as essential.