The Justice League, or Justice League of America (JLA), is a group of superheroes appearing in American comic books published by DC Comics. The team first appeared in The Brave and the Bold #28 (March 1960). Writer Gardner Fox conceived the team as a revival of the Justice Society of America, a similar team from DC Comics from the 1940s which had been pulled out of print due to a decline in sales. The Justice League is an all-star ensemble cast of established superhero characters from DC Comics' portfolio. Diegetically, these superheroes usually operate independently but occasionally assemble as a team to tackle especially formidable villains. This is in contrast to certain other superhero teams such as the Doom Patrol or Marvel’s X-Men whose characters were created specifically to be part of the team, with the team being central to their identity. The cast of the Justice League usually features a few highly popular characters who have their own solo books, such as Superman, Batman, and Wonder Woman, alongside several lesser-known characters who benefit from exposure.

The Justice League was created to boost the profiles and sales of these characters through cross-promotion and helped develop the DC Universe as a shared universe, as it is through teams like the Justice League that the setting's characters regularly interact with each other.

Beyond comic books, the Justice League has been adapted to television shows, films, and video games.

Since 1960, the Justice League has appeared in comic books published by DC Comics (periodicals and graphic novels). These comic books constitute the bulk of Justice League fiction.

In its inception, the Justice League was a revival of the Justice Society of America, created by editor Sheldon Mayer and writer Gardner Fox in 1940. After World War II, superheroes fell out of popularity, which led to the cancellation of many characters, including the Justice Society, which last appeared in All-Star Comics #57 (March 1951). A few years later, sales rose again, and DC Comics revived some of these retired characters, reinventing a few of them in the process. Editor Julius Schwartz asked writer Gardner Fox to reintroduce the Justice Society of America. Schwartz decided to rename it the "Justice League of America" because he felt "League" would appeal better to young readers, evoking sports organizations such as the National League. The Justice League of America debuted in The Brave and the Bold #28 (March 1960), and after two further appearances in that title, got its own series, which quickly became one of the company's best-selling titles. This led DC Comics to create a bunch of other superhero teams, such as the Teen Titans. Marvel Comics, a rival comic book publisher, noticed the Justice League's success and created the Avengers and the Fantastic Four.

The initial Justice League lineup included seven of DC Comics' superheroes who were regularly published at that time: Superman, Batman, Aquaman, the Flash, Green Lantern, the Martian Manhunter, and Wonder Woman. Fox also created a new, non-superhero character called Snapper Carr that was intended to represent DC's teenage readership and joined the League as an Honorary member in their debut story. While Superman and Batman were included in the Justice League's initial lineup, they were largely absent from the League's early stories, playing only minor roles as the pair were already starring together in DC's World's Finest Comics and Fox was worried the two more famous heroes would detract attention from their less popular teammates. As the series went on however, Superman and Batman became more and more present as readers increasingly demanded to see more of them in the League's stories. The team roster would quickly expand with the Green Arrow, the Atom and Hawkman being added to the team over the next four years.

In the Justice Society stories from the 1940s (in All-Star Comics), the Justice Society was used more as a framing device for its members' solo adventures. The stories tended to have the following structure: the Justice Society meets to discuss some new menace, they split up to undertake individual missions that somehow connect to that menace, and finally regroup for the showdown with the main villain. In the 1940s, most comic books were anthologies, and All-Star Comics was in practice not a major deviation from that. By contrast, the Justice League worked together more closely in their stories, thereby having a stronger identity as a team.

In another change from the Justice Society stories of the 1940s, Batman and Superman were regular members of the cast, not mere "honorary members" who made occasional cameos.