Watch Dogs: Legion is a 2020 action-adventure game developed by Ubisoft Toronto and published by Ubisoft. It is the sequel to 2016's Watch Dogs 2 and the third installment in the Watch Dogs series. Set within a fictionalised representation of a futuristic, dystopian London, the game's story follows the hacker syndicate DedSec as they seek to clear their names after being framed for a series of terrorist bombings. While searching for the true culprits, DedSec also attempt to liberate London's citizens from the control of Albion, an oppressive private military company that has turned the city into a surveillance state following the bombings.

While the core gameplay is similar to its predecessors, consisting of a combination of shooting, driving, stealth, and hacking puzzles, Legion introduces a multiple playable characters system, allowing players to recruit virtually any non-player character found in the game's open world. Each playable character has their own unique skills and backgrounds, and can be lost permanently if players enable the option of permadeath before starting a new game. There are multiple ways to complete missions depending on which playable character is selected. In March 2021, a cooperative multiplayer mode was added to the game, allowing up to four players to complete missions or explore London together.

Watch Dogs: Legion was released for PlayStation 4, Windows, Xbox One, and Stadia on 29 October 2020 and as a launch title for Xbox Series X/S and PlayStation 5 in November. Upon release, the game received mixed reviews from critics. They were polarized over the multiple playable characters aspect, with some appreciating its diversity and the inclusion of permadeath for allowing emotional attachment from players, while others criticised the characters' lack of personality and the imbalance between their abilities. Criticism was further aimed at the game's world, driving mechanics, inconsistent difficulty, repetitive missions, online features and technical problems.

Ubisoft supported Legion after its launch, releasing a number of updates for both the single-player and multiplayer modes that added new missions, game modes, and playable characters; a crossover event with the Assassin's Creed franchise; and a paid story expansion, Bloodline, which continues the storylines of Aiden Pearce, the protagonist of the first Watch Dogs game, and Wrench, a major supporting character from Watch Dogs 2.

Watch Dogs: Legion is an action-adventure game played from a third-person perspective, and taking place within an open world setting based upon London, which can be explored either on foot─utilizing parkour moves─vehicles, or fast-travelling via the city's Underground stations. Eight of London's Boroughs are represented in game: Westminster, Wandsworth (specifically the Nine Elms area), Lambeth, Southwark, Camden, Islington, Hackney and Tower Hamlets, in addition to the City of London. The game is composed of several missions, including those that progress the main story, liberation missions aimed at freeing the city's boroughs featured in the setting, recruitment missions for new playable characters, and various side-activities, with players able to freely pursue a mission or activity, or explore the city for secrets and collectibles. Each mission's objectives can be handled via one or several different approaches: an open-combat approach utilizing a variety of weapons; a stealth approach utilizing the environment to avoid detection and monitoring enemy patterns; or a hacking approach using any hackable object to subdue enemies with traps or distractions, while seeking out objectives via cameras and remotely accessing them. Combat includes a mixture of gun fights─involving lethal and non-lethal firearms─and hand-to-hand combat moves, with enemies making use of different methods depending on how the player acts against them in combat (e.g., a guard hit with a punch will use melee attacks, but will begin shooting if the player draws their firearm). Players can be pursued by enemies when escaping, including hostile drones, but can lose them by utilizing hack-able environmental objects (e.g., vents) and avoiding line of sight with pursuers.

Unlike previous games in the series, Legion features the ability to use multiple characters during a playthrough, each of whom can be recruited from around the game's setting. While the player must choose a character to begin with after the story's prologue chapter, others may be recruited upon completing the initial story missions of the game from anywhere around the game's setting, which can include those working for hostile factions. Those recruited become operatives that the player can freely switch to at any time, as well as customize with different clothing options, with each recruit-able character maintaining their own lifestyle and occupation when not active (e.g., spending time drinking at a pub). Each character that can be recruited has different traits and skills, based upon their background─a spy operative has access to a silenced pistol and can summon a special spy vehicle to travel around with, armed with rockets; a hooligan operative can summon friends to help in a fist-fight; a builder operative can make use of large drones for heavy-lifting and a nail-gun for combat; while an "adrenaline junkie" operative can deal more damage, but risk the possibility of being knocked out/dying at random moments. Operatives can gain experience when used by the player, which allows them to gain additional skills and abilities to improve them, with the player able to provide additional upgrades for all characters by spending "tech points"─a collectible scattered around the city, which can be spent on weapon and gadget upgrades. In addition to standard recruitable NPCs, the player can also acquire special NPCs to their roster, known as "Prestige Operatives"; these unique characters possess exceptional weapons and gain access to stronger perks as they improve in level than standard operatives.

All potential recruits have an additional statistic, which details whether they can be recruited when approached─their thoughts on DedSec. Some recruits may not join if either they favour those that oppose them (such as a hostile faction), if the player has a character in their roster whom they hate, or if DedSec did something to harm another NPC they have good relations with. If a recruit can be brought in, players will be required to complete a mission from them related to a problem they need resolving. Examples of such a mission include sneaking into a government building to find a missing person, recovering confiscated or stolen equipment or simply helping the potential recruit determine why they are experiencing invasive surveillance. Any character that can be recruited can be killed during a playthrough, whether in combat, accidental death, or from their own traits, and permanently removed from the player's roster of playable characters if the player has the permadeath option enabled. If in permadeath mode the player loses all their characters from death or arrest, the game ends. In games with permadeath disabled, operatives will be incarcerated or hospitalised after being arrested or 'critically injured'; the time these characters spend being unable to be used can be reduced if the player recruits certain characters, such as medical or legal staff. In addition, some operatives may still die permanently, but only if they have certain traits that lead to a random and unexpected death.

The online component of the game, introduced in March 2021, allows for four-player cooperative gameplay, which aimed to share progression between the single-player and multiplayer modes. The multiplayer experience offers several different activities for players to engage in, including city events, co-operative missions (including the more complex "Tactical Ops"), and the "Spiderbot Arena" competitive mode, where players controlling miniature spiderbot gadgets fight in free for all matches. The asymmetrical multiplayer mode "Invasion" from the previous two Watch Dogs games made a return several months after release, with several changes.