Euthyphro, by Plato, is a Socratic dialogue whose events occur in the weeks before the trial of Socrates (399 BC), between Socrates and Euthyphro. The dialogue covers subjects such as the meaning of piety and justice.

The dialogue is set near the king-archon's court, where the two men encounter each other. They are both there for preliminary hearings before possible trials. The argument of this dialogue is based largely on “definition by division”. Socrates goads Euthyphro to offer one definition after another for the word ‘piety’. The hope is to use a clear definition as the basis for Euthyphro to teach Socrates the answer to the question, “What is piety?”, ostensibly so that Socrates can use this to defend himself against the charge of impiety.