Polycrates of Sparta was a 5th-century BCE Greek historian from Laconia. No details of his life, background, or education survive beyond this geographical identification.

His sole known work is the lost Lacedaemonion Politeia, or The Constitution of the Lacedaemonians. It survives only in fragments and later references, and is an early example of the politeia genre describing a city-state's laws and institutions. Polycrates provides an early internal perspective on Sparta.

His work is cited by later authors like Xenophon and likely informed understanding of Spartan customs, education, and law, contrasting with external accounts.