"Crisis on Infinite Earths" is the sixth Arrowverse crossover event, featuring 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. The events of the Black Lightning episode "The Book of Resistance: Chapter Four: Earth Crisis" (which aired between Batwoman and The Flash) and a two-issue comic book with characters and concepts unused in the live-action episodes also tied into the event.

"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 some aspects of the Arrowverse being rebooted, affecting all of the series.

Initial references to the crossover began in 2014 with The Flash's pilot episode. The adaptation began in earnest during the development of "Elseworlds", and the crossover's title was revealed at the end of "Elseworlds" in December 2018. Casting was announced in mid-2019 and included actors who previously portrayed DC characters in other media, such as Burt Ward and Kevin Conroy. Cress Williams from The CW series Black Lightning crossed over with the Arrowverse for the first time, and other actors reprised their roles from various DC film and television series. The event was filmed from the end of September to the beginning of November 2019.

"Crisis on Infinite Earths" was critically praised for its scope, ambition, and the many cameos, though the fate of Oliver Queen had a mixed reception. The crossover proved popular, as each episode gave season-high ratings to its corresponding series. A two-episode aftershow, Crisis Aftermath hosted by Kevin Smith, aired after parts one and three to explore the crossover's events. "Crisis on Infinite Earths" was intended to be followed by a crossover between Batwoman and Superman & Lois in 2021, but this did not occur because of the COVID-19 pandemic, being replaced informally by David Ramsey appearing as John Diggle on multiple Arrowverse series. The next crossover, "Armageddon", occurs over the first five episodes of the eighth season of The Flash in November and December 2021.