The Arcadian League is a federal league of city-states in ancient Greece.

It combines the various cities of Arcadia, in the Peloponnese, into a single state.

The league is founded in 370 BCE, taking advantage of the decreased power of Sparta, which had previously dominated and controlled Arcadia.

Mantinea, a city that had suffered under Spartan dominance, is particularly prominent in pushing for its founding.

The league has its capital at the newly founded city of Megalopolis, where an assembly of ten thousand meets as its governing body.Although initially successful in resisting Spartan influence in Arcadia, the league is soon divided in the power struggles that engulf Greece in the 4th century BCE.

Thebes, which had been instrumental in the founding of the league, soon comes into conflict with Mantinea.

At the Battle of Mantinea (362 BCE), the cities of the league fight against each other, Mantinea fighting alongside Sparta and Athens, while Tegea and others side with Thebes.

Nonetheless, the league seems to have endured in some form down into the 3rd century.