Karl Popper's main work in social philosophy primarily addresses the history of historicism, which is the idea of a lawful historical progression, as seen in Plato (Volume I) as well as in Hegel, Marx, and their successors (Volume II). It also contains a multitude of discussions on epistemological, philosophical, ethical, and political questions that remain highly relevant today. The fact that this book has been translated into 23 languages since 1945 underscores that Popper's 'contribution to the war' is much more than an original engagement with philosophical systems from antiquity to the present. The theory of the open society, which advocates for the continuous gradual improvement of institutions in parliamentary-democratic societies, is developed so thoroughly in these two volumes that all those interested in the foundation and advancement of civil societies can benefit.