This book offers a careful re-reading of Popper's classic falsificationist demarcation of science, stressing its institutional aspects. Popper's social thinking about science, individuals, institutions, and rationality is tracked through The Poverty of Historicism and The Open Society and Its Enemies as he criticises and improves his earlier work. New links are established between the works of the 1935-1945 period, revealing them as a source for criticism of the institutions and governance of science.