In most of the DC Comics media, the Multiverse is a "cosmic construct" that is composed of the many universes the stories of DC media take place in. The worlds within the multiverse share a space and fate in common, and its structure has changed several times in the history of DC Comics.

The concept of a universe and a multiverse in which the fictional stories take place was loosely established during the Golden Age of Comic Books (1938–1956). With the publication of All-Star Comics #3 in 1940, the first crossover between characters occurred with the creation of the Justice Society of America (JSA), which presented the first superhero team with characters appearing in other publications (comic strips and anthology titles) to bring attention to less-known characters. This established the first shared "universe", as all these heroes now lived in the same world. Prior to this publication, characters from the different comic books seemingly existed in different worlds.^{[citation needed]}

Later, Wonder Woman #59 (May 1953) presented DC Comics' first story depicting a parallel "mirror" world. Wonder Woman is transported to a twin Earth where she meets Tara Terruna, who is exactly like her. Tara Terruna means "Wonder Woman" in the native language of that world. Wonder Woman describes this world as being a twin world existing alongside Earth with duplicates of everyone but with a different development. The concept of different versions of the world and its heroes was revisited in the pages of Wonder Woman a few times later.

Led by editor Julius Schwartz and writer Gardner Fox, DC Comics' superheroes were given a "reboot" with the publication of Showcase #4 in 1956, where a new version of the Flash made his first appearance. This is considered the beginning period of the Silver Age of Comic Books. The success of this new Flash led to the creation of new incarnations of the Golden Age characters who only shared the names and powers but had different secret identities, origins and stories. Later, new versions of other heroes, Superman, Batman and Wonder Woman, were also restarted by retelling their origins but keeping their secret identities. Fox, who worked before in the creation of the JSA, where other heroes met for the first time, created the story "Flash of Two Worlds" in The Flash #123 (1961), where Barry Allen, the new Flash, is transported to the Earth where the original Flash, Jay Garrick, existed. To Barry, Jay Garrick's world was a work of fiction as it was in the real world. This story not only presented the encounter of two worlds and the existence of the Multiverse for the first time, but it also presented key features of the Multiverse: all the universes vibrate at a specific frequency which keeps them separated; these "barriers" could be trespassed by "tuning" to that vibration. Because people could also "tune-in" these worlds in dreams, some people wrote comic books with the stories from those worlds they dreamed, which explained why Barry knew about Jay as a fictional character.

The success of this story led to the first team crossover between the new Justice League of America (JLA) and the Golden Age JSA, in the stories "Crisis on Earth-One" (Justice League of America #21) and "Crisis on Earth-Two" (Justice League of America #22), published in late 1963. This story arc started the tradition of a yearly crossover between the JLA and the JSA, and established the concept of a Multiverse and the designation of names, Earth-One being the JLA reality and Earth-Two the JSA reality. The success of these crossovers spawned publications telling the further stories of the Golden Age heroes in the present-day parting from many of the stories told, thus establishing a more defined continuity for every universe.

This concept of parallel Earths with differences in locations, persons and historical events became a very important ingredient within DC Comics' publications. It helped (among other things) to explain continuity errors, to retell and retcon stories, and to incorporate foreign elements that could actively interact with everything else and allow them to have an "existence". Continuity flaws between the established Earth-Two and several stories from the Golden Age were given separate Earths. "Imaginary" stories and sometime divergences of Earth-One were given also separate realities (such as Earth-B and Earth-A). In addition to the stories appearing mainly in the pages of JLA that created new Earths, the acquisition of other comic book companies and characters by DC Comics incorporated these new properties as Earths in the Multiverse which would interact several times with the "main" Earths, One and Two; two of the most notable being Earth-S for the Fawcett Comics characters, and Earth-X for the Quality Comics characters. By the 1970s, everything that was published or related officially to DC Comics' titles could become part of the Multiverse, although much of it remained largely uncatalogued.

The names of the worlds were usually in the format Earth, hyphen, spelled numeral/letter/name. In the case of worlds with numerals, the "rule" of spelling the number was not always followed, even within the pages of the same issue.

As the 50th anniversary of DC Comics drew near, major events were proposed for the celebration: an encyclopedia (Who's Who in the DC Universe) and a crossover of the ages, characters, and worlds appearing in DC's comics. As told in the letter section of Crisis on Infinite Earths #1, as the research started in the late 1970s, it became evident that there were many flaws in continuity. The way used to circumvent some of these errors was the "Multiple Earths", which also showed a chaotic nature that brought even more continuity problems that were not easily explained or were simply left unexplained. Examples of this included: 1) the Black Canary of Earth-One being the daughter of the original Black Canary, who was a resident of Earth-Two, and 2) the existence of Golden Age comic books on Earth-One and the people not noticing that some of the characters in those comic books existed in "real life". In addition, many universes had multiple alternate timelines, such as Kamandi and the Legion of Super-Heroes both being from Earth-One.