Earth-One is a name given to two fictional universes that have appeared in American comic book stories published by DC Comics. The first Earth-One was given its name in Justice League of America #21, after The Flash #123 explained how Golden Age (Earth-Two) versions of characters such as the Flash could appear in stories with their Silver Age counterparts. This Earth-One continuity included the DC Silver Age heroes, including the Justice League of America.

Earth-Two is a setting for stories appearing in American comic books published by DC Comics. First appearing in The Flash #123 (1961), Earth-Two was created to explain differences between the original Golden Age and then-current Silver Age versions of characters such as the Flash, and how the current (Earth-One) versions could appear in stories alongside earlier versions of the same character concepts. Earth-Two includes DC Golden Age heroes, including the Justice Society of America, whose careers began at the dawn of World War II, concurrently with their first appearances in comics. Earth-Two, along with the four other surviving Earths of the DC Multiverse, were merged into one in the 1985 miniseries Crisis on Infinite Earths. However, following the events of Infinite Crisis, the Multiverse was reborn, although the subsequent Earth-Two was not the same as its pre-Crisis equivalent.