The Open Society and Its Enemies is an influential two-volume work by Karl Popper, written during the second world war. Failing to find a publisher in the United States, it was first printed in London, in 1945.

In The Open Society and Its Enemies, Popper developed a critique of historicism and a defence of the open society, liberal democracy. The book comes in 2 volumes, volume 1 subtitled "The Spell of Plato", volume 2 "The High Tide of Prophecy Aftermath".

Volume 1 is mainly a critique of Plato's political ideas. Popper acknowledges Plato's merits as a philosopher, and never questions Plato's immense influence on philosophy and society. However, he argues that this influence was for the most part foul.

Plato's ideas are separated from Socrates', which are humanitarian and democratic. Popper accuses Plato of betraying Socrates when using him as a speaker in some of his later dialogues, where "Sokrates" touts ideas of totalitarianism (see also: Socratic problem). Popper points out that Plato's writing, for example The Republic or Laws, are authoritarian and totalitarian, a fact that was often idealised away in mainstream interpretations of Plato at the time of writing. Plato did a great job in observing and analysing the inner workings of society. However, Plato's conclusions and advice on how to create the perfect society are dangerous at best. According to Popper, Plato's works perfectly reflect his ambitions to become "Philosopher-King". Plato's sociology is brilliant in the sense that his work did extremely well in promoting a totalitarian society thoughout the centuries and until modern times.

In volume 2, Popper moves on to criticise Hegel and Marx, tracing back their ideas to Aristotle.