Phantasy Star (ファンタシースター Fantashī Sutā^?) is a series of console role-playing video games and other supplementary media created by Sega. The series debuted in 1987 on the Sega Master System with Phantasy Star, and continues into the present with Phantasy Star Online 2 and other extensions of the Phantasy Star Online sub-series. Each of the games in the series features a science fantasy setting featuring a cross-genre combination of magic and technology.

The first four games in the series are set in or are related to the planetary system of Algol, and are single-player RPGs. Later titles bearing the Phantasy Star name are for the most part massively multiplayer online games. Phantasy Star Online and Phantasy Star Universe are set in other galaxies; they share certain minor canonical links with the original series, mostly in the recurrence of common themes and antagonists.