The Legends of Tomorrow is part of a shared universe made up of several (ever increasing) CW prime-time shows, plus several animated web series.
There are currently five prime-time shows: The Arrow, The Flash, Supergirl, Legends of Tomorrow, and Black Lightning. (Listed in the order that they premiered.)
(Disclosure: I only watch three of those full time, the other 2 being too dark for me to continue and enjoy. Arrow I have watched sporadically, seeing some parts of a few different seasons. And Black Lightning I watched all of season one, but stopped after that. So there are some holes in my knowledge of those two shows. Luckily, I have you guys to fill in if I miss something!! )
All these shows exist in the same universe. (Edit: Mostly. Black Lightning probably is, but that is unconfirmed.) Characters visit friends on other shows, or start out on one show only to become a regular on a different one. But, this universe follows the multiple worlds theory, and some characters have the ability to travel to parallel Earths. The Arrow, Flash, and Legends all take place on the same earth, though characters on the Flash regularly interact with people from a number of different Earths. This includes Supergirl, who exists on her own Earth, and thus crosses over much more infrequently. (This is a remnant of the show beginning on CBS, before it moved to the CW and got folded into the shared universe.) Black Lightning (as of season one) appears to be on it’s own Earth unvisited by any of the other shows, and has not crossed over with any. (To my knowledge, as of season 1.) I don’t know if they plan to keep it that way or not.
Every year they do a big crossover between multiple shows, last year being the most ambitious (and complicated), bringing four shows together in one big story. (This was all the shows that were on the air at the time). They just about managed to include characters from all four shows, but it was also totally insane. This year (this week actually, starting tonight), they are only crossing over three shows: The Flash, Arrow, and Supergirl.
Since they are leaving the Legends OUT of the big crossover, The Legends decided they would still do a crossover, all by themselves!! Yep, they are doing a crossover with different versions of THEMSELVES!!!
Last week’s episode 4x07 set up a reality bending temporal paradox. Reality has basically broken around the Legends, and they … well, change! Here comes episode 4x08 - Legends of To-Meow-Meow!!!
(And then hiatus until April, I believe. )
Edited by Sci-Fi Girl, 09 December 2018 - 03:58 PM.