Someone asked for help with the Legion of Super-Heroes a few pages back. Was it
Aizō? I'm not sure. Still. Here's a run down for everyone.
There are "four" versions of the Legion. Each group has its own quirks making it stand out from the rest.
1.)
The Originals: This was the group that's been around the longest. They date back into the late 50's, but you'll get lost in a ton of early Silver Age stuff if you try to follow them from this point. The only notable run is Jim Shooter's, but even that is arguably skippable and Shooter has a stronger run worth following later on.
The first writer to really glom on to the Legion and make them into something big is Paul Levitz. He hops onto the team with
Superboy and the Legion of Super-Heroes #225, and writes the book fairly consistently until 251. After that he goes away for a while, and since this is way too much history to recap we're gonna skip ahead a bit. The Legion of Super-Heroes don't get their own comic book until Superboy and the Legion of Super-Heroes transforms into "The Legion of Super-Heroes (vol. 2)". It's confusing, but they keep the same numbering so their first ongoing issue is "The Legion of Super-Heroes #259". Volume 1 by the way is a random mini-series collecting older LOSH tales.
Anyway, Paul Levitz comes back for LOSH #281 and stays on the book for ages after this. This is where he eventually does The Great Darkness Saga, which happens around LOSH v2 290. He builds the team up over time until they become popular enough to support two different ongoings, so in 1984 DC launches
The Legion of Super-Heroes vol. 3 #1 with Levitz and Keith Giffen handling the writing, while LOSH v2 becomes
Tales of the Legion of Super-Heroes with 314. Things were going well here, but COIE would eventually knock things off the rails, as John Byrne's new origin for Superman set things up so that Superboy was never a thing, and so he was never a member of the Legion, something which had to be explained. The attempt to do that led to the introduction of a "pocket universe" where "their" Superboy was supposedly from, and he eventually died during some massive crossover.
Legion of Super-Heroes v3 ended at #63, while Tales of the Legion stops at 325. (Tales continues but only republishing reprints after this.) After this, Levitz is out the door and you've got Keith Giffen taking over the characters for what happens next.
Legion of Super-Heroes vol. 4 #1 is set five years after the last story of Levitz/Giffen, The "Magic Wars". Giffen's time on the characters, alongside Tom and Mary Bierbaum, is controversial for a lot of reasons, chief of which being he took the idyllic future of the Legion and made it a much more dark, cynical place. This is also where you get the retcon for Mon-El becoming the inspiration for the Legion, because my understanding is DC wanted no references to Superman or Superboy
at all in the Legion. They were weird back then.
The other reason people got frustrated is Giffen introduced a bunch of clones: the Batch SW6, who'd been created by the Dominators. They got their own book, a light-hearted comic known as Legionnaires. This was supposed to be the Legion's own Clone Saga basically, because he was fully intending to confirm the clones as the real ones. Fortunately DC's constant big events made that an impossibility. Zero Hour would force the first proper reboot on the team in 1994, putting an end to 5YL.
2.) Post Zero Hour: Mark Waid, Tom McCraw, and Tom Peyer headed up a reboot of the Legion in 1994. At the time they were called the Archie Legion, thanks to Jeffrey Moy's lighter, more cartoony artstyle. This wouldn't have been out of place as a part of the DCAU. Yet again they didn't really reboot the numbering, so post Zero-Hour starts with
Legionnaires Vol. 1 #19 and
Legion of Super-Heroes vol. 4 #63. This book stuck around for the better part of the 90's, and spent most of its time reestablishing the Legion and their villains in this new universe. This is where you get characters like XS btw.
This is my personal favorite incarnation of the Legion, not only because its the one I grew up with, but also because it was the most diverse both racially and artistically. This run lasted up until #125 and 81. It's all fun, but most of it isn't collected. The very beginning is, and the last trade which starts Dan Abnett and Andy Lanning is though.
Speaking of, DnA take over the book after this, but first they do Legion Lost and Legion Worlds. LL tells the story of a group of Legionnaires lost on the other side of the universe, while Worlds talks about the Legionnaires who were left in the United Planets.
This all culminates in
The Legion, a 36 issue run that caps off the Post Zero Hour era of the team. The stories are slightly darker along the lines of the 5YL stuff, but the story is better than ever. Well worth getting the whole thing.
3.) Threeboot: For whatever reason Dan Didio decided the Post Zero Hour Legion needed to go away and we needed a reboot. So he called up Mark Waid (again) and had him come up with a new vision for the heroes of tomorrow. This is where we get the threeboot team, set in a much more realistic version of the future, where all the heroes of the past have gone into legend, and may "never have existed at all". (This would eventually be explained away by saying the Threeboot version of the team belonged to Earth-Prime.) If anyone's keeping count, this is
The Legion of Super-Heroes Vol. 5.
Mark stays on this book for roughly 30 issues or so, with the first half introducing his new Legion--a group of teens striking back against an oppressive regime of adults, and coining the "legendary" phrase, "Eat it, Grandpa" for the team's new rallying cry. The second half of his book brought Supergirl in for a sales boost, but while this might've worked, DC kinda shot themselves in the foot by showing the "original Legion", giving old school fans no reason to even continue with the newer team.
Despite Waid's rather silly characterization of teens, the first 30 issues of this are fairly strong. But what I found much stronger were Jim Shooter's issues, which ran from #37 to 50, the final issue. Jim not only had some inspired ideas for this universe, but this gave us what I believe is Francis Manapul's first big two assignment. It's beautiful stuff even here, and well worth tracking down if you're interested.
4.) Fourth Coming: Shortly after Infinite Crisis, Geoff Johns thought it'd be a good idea to revive the Legion. The "original" Legion everyone loved. So one of the first storylines he did alongside Brad Meltzer was a JLA/JSA crossover called The Lightning Saga. This would eventually lead into Johns' Action Comics Legion story, "Superman and the Legion of Super-Heroes", and conclude with Legion of Three Worlds, which took all three previous versions (plus the others) and gave them one big, "final" story.
After this, Johns was thought to write the Legion, but with him writing multiple ongoings he was never able to find the time. He did Adventure Comics, a Superboy book with a Legion of Super-Heroes back up, for six issues, before leaving the title to Jeff Lemire. The Legion went back to Paul Levitz, but none of these stories are good. The team would survive the New 52, but those stories are worse, and the book finally came to an end in 2012 or so. Basically, only pay attention to the Johns' trilogy from this era.
Hope that all helps as far as figuring out the chronology of things. If anyone needs more clarification, just let me know.