"Flash of Two Worlds!" is a landmark comic book story that was published in The Flash #123. It introduces Earth-Two, and more generally the concept of the multiverse, to DC Comics. The story was written by Gardner Fox under the editorial guidance of Julius Schwartz, and illustrated by Carmine Infantino. In 2009, DC Comics released a new digitally remastered graphic novel collection, DC Comics Classics Library: The Flash of Two Worlds. It features the classic flagship story and other subsequent pre-Crisis Flash material.

The Flash is an ongoing American comic book series featuring the DC Comics superhero of the same name. Throughout its publication, the series has primarily focused on two characters who have worn the mantle of the Flash: Barry Allen, the second Flash, and Wally West, the third Flash. The series began at issue #105, picking up its issue numbering from the anthology series Flash Comics which had featured Jay Garrick as the first Flash.