"Crisis on Infinite Earths" is the sixth annual Arrowverse crossover event, featuring episodes of the live-action television series Supergirl, Batwoman, The Flash, Arrow, and Legends of Tomorrow on The CW. The Supergirl, Batwoman, and The Flash episodes air in December 2019, while the Arrow and Legends of Tomorrow episodes will air in January 2020. Additionally, events in the Black Lightning episode "The Book of Resistance: Chapter Four: Earth Crisis", airing between Batwoman and The Flash, will also tie-in to the crossover. A two-issue comic will also tie into the crossover, featuring characters and concepts not able to appear in the live-action episodes.

"Crisis on Infinite Earths", which is inspired by the comic of the same name, continues plot lines established in the previous crossover, "Elseworlds". Moreover, the preceding episodes of Arrow season eight and much of The Flash season six served as a prelude to the crossover. In "Crisis on Infinite Earths", the Monitor gathers Green Arrow, the Flash, Supergirl, Batwoman, the Legends, and several "Paragons" from throughout the multiverse to stop the Anti-Monitor from destroying all of reality.

Allusions to "Crisis on Infinite Earths" began in 2014, with the pilot episode of The Flash. The adaption of the comic storyline began in earnest during the development of "Elseworlds", with the crossover title revealed at the end of "Elseworlds" in December 2018. In mid-2019, multiple castings were revealed, including that actors who previously portrayed DC characters in other media, such as Burt Ward and Kevin Conroy, would appear in the crossover. "Crisis on Infinite Earths" will also see cast members from fellow CW series Black Lightning appear and cross over with the Arrowverse for the first time, along with actors reprising their roles from various DC film and television series. Filming took place from the end of September 2019 until the beginning of November 2019.