Arrowverse appearances

The television series Supergirl and Superman & Lois are a part of the "Arrowverse", a television franchise that is based on characters that appear in publications by DC Comics. The shared multiverse is akin to the DC universe in their comic books, which has had crossover plot elements, settings, and characters. Before the crossover Crisis on Infinite Earths, Supergirl took place on Earth-38 while the other Arrowverse shows took place on Earth-1. After the Crisis, all the shows were combined into a single universe called Earth-Prime.

Superman & Lois takes place after the Crisis.

Crossovers with Other Shows

Worlds Finest (2016)

"Worlds Finest" is the eighteenth episode of the first season of Supergirl, and the eighteenth episode overall. It aired on March 28, 2016. It acts as a crossover between Supergirl and The Flash, bringing the series into the Arrowverse.

Invasion! (2016)

Invasion! is the name of the third annual Arrowverse crossover event between Supergirl, The Flash, Arrow and DC's Legends of Tomorrow​. The crossover aired over four nights from November 28 to December 1, 2016. In the crossover, Barry Allen recruits Kara to help his team, Oliver Queen and his team, and the Legends to defeat the alien race known as the Dominators.

Duet (2017)

"Duet" is the seventeenth episode of the third season of The Flash, and the sixty-third episode overall. It aired on March 21, 2017. It is the main part of the musical crossover between The Flash and Supergirl​, which was set up at the end of the sixteenth episode of the second season of Supergirl.

Crisis on Earth-X (2017)

"Crisis on Earth-X" is the fourth annual Arrowverse crossover event, featuring episodes of the live-action television series Supergirl, Arrow, The Flash, and Legends of Tomorrow on The CW. The crossover began on November 27, 2017, with Supergirl and Arrow, and concluded on November 28, with The Flash and Legends of Tomorrow. In "Crisis on Earth-X", Barry Allen and Iris West's friends come to Central City for their wedding, only for the proceedings to be interrupted by interlopers from the analogous universe of Earth-X, where the Axis powers claimed victory in World War II.

Elseworlds (2018)

"Elseworlds" is the fifth annual Arrowverse crossover event that features episodes of the live-action television series The Flash, Arrow, and Supergirl on The CW. The crossover event began on December 9, 2018, with The Flash, continued on Arrow on December 10, and concluded on Supergirl on December 11. "Elseworlds" introduces the characters Batwoman and Lois Lane, and the fictional Gotham City, to the universe. In the crossover, Green Arrow, Flash, and Supergirl are drawn to Gotham City to confront Dr. John Deegan over his work at Arkham Asylum.

Crisis on Infinite Earths (2019-2020)

"Crisis on Infinite Earths" is the sixth annual Arrowverse crossover event and features episodes of the television series Supergirl, Batwoman, The Flash, Arrow, and Legends of Tomorrow on The CW. The Supergirl, Batwoman, and The Flash episodes aired in December 2019 while the Arrow and Legends of Tomorrow episodes aired in January 2020. "Crisis on Infinite Earths", inspired by the comic of the same name, continues plotlines established in the previous crossover, "Elseworlds". The preceding episodes of Arrow season eight and much of The Flash season six serve as a prelude to the crossover. In "Crisis", the Monitor gathers Green Arrow, the Flash, Supergirl, Batwoman, Sara Lance, Ray Palmer, and several others from throughout the multiverse to stop the Anti-Monitor from destroying reality. The crossover's events result in the Arrowverse being rebooted, affecting all of the series.

For the event, both Brandon Routh and Tom Welling made brief cameos. Routh portrays a Kingdom Come-inspired version of the character from the Christopher Reeve films (designated as Earth-96) while Welling reprised his role for the first time in eight years after Smallville (designated as Earth-167) concluded.

Ezra Miller made a guest appearance on "Hour Four" of the special as The Flash of the 2017 theatrical and 2021 director's cut of Justice League, confirming the DC film universe and the "Snyder DC Trilogy" (which includes Man of Steel and Batman v Superman: Dawn of Justice) as part of the same multiverse.