DC Continuity Crash Course
Navigating the DC universe can be tricky, even for longtime fans. Knowing what is considered "canon" can be even trickier, especially when the present canon is constantly changing, but there is a main timeline comics generally follow. This guide will take you through the basics as well as define some terms you may frequently come across in the fandom.
The first thing fans should know is The Multiverse exists in DC continuity, meaning there are several different realities that may show up or be referenced in comics. Most of these realities receive an "Earth" designation, such as Earth-1 or Earth-12. The current DC canon takes place on Earth-0.
Now, wouldn't it be nice if we could stop there? Sigh. For better or for worse, DC loves reality altering events, and Earth-0 has experienced its fair share of them with the most critical ones being Crisis on Infinite Earths and Flashpoint.
Crisis on Infinite Earths (1986) was a multiversal event that effectively rebooted the timeline and began an era of Earth-0 called New Earth or Post-Crisis. Unless otherwise re-canonized through comics published in the Post-Crisis era, stories published prior to the event (dubbed Pre-Crisis) were no longer considered canon.
Flashpoint (2011) was an event that ended the New Earth timeline and began the Prime Earth timeline. As of today, this is the timeline Earth-0 is still currently in.
Prime Earth can be broken up into various branding eras or titles, each one fairly recognizable by characteristic logos being printed on the covers of single issues and graphic novels alike, but you can also identify them by publishing date.
The New 52 (2011) marks the beginning of Prime Earth. This was a controversial era of DC wherein several things from New Earth were retconned. Many characters' origin stories were revised, each to varying degrees.
Rebirth (2016) served as a soft "reboot" to the New 52 where several elements from New Earth were re-integrated into the current timeline (restoring many old and beloved origin stories/retconning poorly received New 52 origins) while still keeping many critical plot points from the New 52 canon.
Infinite Frontier (2021) continues directly from Rebirth. Rather than rebooting anything, it integrates some more elements of the New Earth timeline and leads directly into DC's current branding initiative: Dawn of DC.
As a reminder, not everything from Post-Crisis has been re-canonized with Rebirth and Infinite Frontier; this is a common misconception. Some events in these comics happen in a way that make it impossible for certain Post-Crisis stories to have happened. Likewise, not everything from New 52 has been retconned either. The specifics, unfortunately, are unique to each character, and truly the best understanding of them is achieved through reading the comics. The DC Wiki page, however, generally does a good job explaining a character's origins and their current canon. They also typically list retcons and inconsistencies in the character's page notes.
But wait! I hear people say all the time. What about stories that don't fit the branding, like Injustice, DC vs. Vampires, or Wayne Family Adventures? Aren't they still DC?
Just because something is published by DC (or in association with DC) does not mean the story is canon. In fact, DC frequently publishes non-canon stories (often called Elseworlds) to tell a story they otherwise can't in the main timeline. These stories are usually fairly easy to identify, especially if you're familiar with the main comics. They may take the characters to a different setting, change their origin stories, change their personalities, change their relationships, give them a new family or children– really the possibilities are endless. But the bottom line is, because these are non-canon stories, any events or (mis)characterizations you see in these do not apply to their mainstream counterparts. I realize this probably seems intuitive, but I have seen enough people conflate the two to the point I feel I have to clarify.