Phaedo, also known to ancient readers as On The Soul, is deservedly one of the best known works of Greek literature, along with the Republic and the Symposium. The philosophical subject of the dialogue is the immortality of the soul. It is set in the last hours prior to the death of Socrates.

In the dialogue, Socrates discusses the nature of the afterlife on his last day before being executed by drinking hemlock. Socrates has been imprisoned and sentenced to death by an Athenian jury for not believing in the gods of the state (though some scholars think it was more for his support of "philosopher kings" as opposed to democracy) and for corrupting the youth of the city.

The Phaedo is generally considered one of Plato's greatest works.