The Greco-Persian Wars are a series of conflicts between several Greek city-states and the Persian Empire that start in 499 BCE and last until 448 BCE.

The expression "Persian Wars" usually refers to both Persian invasions of the Greek mainland in 490 BCE and in 480-479 BCE; in both cases, the allied Greeks successfully repel the invasions.

Not all Greeks fight against the Persians; some are neutral and others allied with Persia, especially as its massive armies approach.