Young Justice: Outsiders is the third season of the American animated superhero series Young Justice, developed by Brandon Vietti and Greg Weisman. The series follows the lives of teenage superheroes and sidekicks who are members of a covert operation group, referred to simply as "The Team", that acts as a young counterpart to the famous adult team, the Justice League. In the second season, Invasion, the Reach revealed the existence of the meta-gene. Following on from these events, the third season focuses on the Team battling metahuman trafficking. It also features the superhero team Outsiders.

Young Justice originally aired on Cartoon Network for two seasons from 2010 to 2013, before being cancelled due to low toy sales and Mattel pulling funding. Following a strong fan campaign and high viewership ratings on Netflix, the series was officially renewed for a third season by Warner Bros. in November 2016. Development on Outsiders began the next month. By July 2017, it was split into two separate sections/arcs, each consisting of 13 episodes, making a total of 26 for the whole season.

The first half of the season was released between January 4 and 25, 2019, on DC's new digital platform, DC Universe, for a total of 13 episodes. The second half of the season, consisting of the remaining 13 episodes, premiered on July 2, 2019. During the Young Justice portion of the DC Universe panel at the 2019 San Diego Comic-Con, Weisman and Vietti announced that production for the fourth season titled Phantoms is already underway to continue the story after Outsiders. The fourth season premiered on HBO Max on October 16, 2021.

The first letter of each episode spells out a hidden phrase: "Prepare the Anti-Life Equation".

In January 2013, Cartoon Network had meetings with potential clients and promotional partners in which they announced their 2013–14 programming lineup with Young Justice being absent. A Warner Bros. Animation representative confirmed in an interview with Newsarama the cancellation of both Young Justice and Green Lantern: The Animated Series, with the DC Nation block replacing the series with Teen Titans Go! and Beware the Batman. While a fan-campaign was created in the hopes of financing continuations for both shows, Warner Bros. halted the campaign in May as they did not believe the goal could be reached.

In December 2013, Kevin Smith and Paul Dini claimed in an episode of Smith's podcast Fatman on Batman, that Young Justice was cancelled due to the program's high female viewership, as network executives did not believe girls would buy toys based on the show. Greg Weisman however denied this rumor and in a January 2016 episode of "The Hip-Hop Nerd" podcast, revealed the real reason why it was canceled. The show's funding was based on a toy deal with the toy company Mattel and due to low toy-sales, Mattel pulled the funding. With no other source of income to replace the money Mattel provided, the series was effectively canceled.

The possibility of Young Justice revival first occurred in early February 2016 when the series' second season was released on Netflix, with Weisman urging fans to watch all episodes "over and over" or buy Blu-rays if they wished for a third season. Weisman later clarified that while neither Warner Bros. nor Netflix had expressed interest in picking up the show for a third season, high viewership on Netflix could motivate Warner Bros. into renewing the show. During June, Weisman revealed that the possibility of Young Justice being renewed was "very real" but noted that fans needed to keep the show trending to convince Warner and Netflix of its potential.

On November 7, 2016, it was officially confirmed by Sam Register, president of Warner Bros. Animation and Warner Digital Series, that Young Justice was renewed for a third season, stating that the dedicated fanbase and "[its] rallying cry for more episodes" resonated with them. It was also confirmed that Weisman and Brandon Vietti would be returning as showrunners.