Polybius is a fictitious 1981 arcade game from an urban legend. The legend describes the game as part of a government-run crowdsourced psychology experiment based in Portland, Oregon. Gameplay supposedly produced intense psychoactive and addictive effects in the player. These few publicly staged arcade machines were said to have been visited periodically by men in black for the purpose of data-mining the machines and analyzing these effects. Supposedly, all of these Polybius arcade machines then disappeared from the arcade market.

Polybius is a 2017 shoot 'em up video game developed and published by Llamasoft. It was released in May 2017 for the PlayStation 4, with PlayStation VR support available. A version for Windows was released in December 2018. The game takes its name and inspiration from the fictitious 1981 arcade game Polybius. It is also inspired by games like TxK and aims to induce the psychological state of flow. It was positively received by critics.