Assassin's Creed Unity is a 2014 action-adventure game developed by Ubisoft Montreal and published by Ubisoft. It was released in November 2014 for PlayStation 4, Windows, and Xbox One, and in December 2020 for Stadia. It is the eighth major installment in the Assassin's Creed series, and the successor to 2013's Assassin's Creed IV: Black Flag. It also has ties to Assassin's Creed Rogue, which was released for the previous generation consoles on the same day as Unity.

The plot is set in a fictional history of real-world events and follows the millennia-old struggle between the Assassins, who fight to preserve peace and free will, and the Templars, who desire peace through control. The framing story is set in the 21st century and features an unidentified and unseen protagonist, who joins the Assassins as an initiate to help them locate the corpse of an 18th-century Templar Grand Master. The main story is set in Paris during the French Revolution from 1789 to 1794, and follows Assassin Arno Dorian and his efforts to expose the true powers behind the Revolution, while seeking revenge against those responsible for his adoptive father's murder. Unity retains the series' third-person open world exploration as well as introducing revamped combat, parkour, and stealth systems. The game also introduces cooperative multiplayer to the Assassin's Creed series, letting up to four players engage in narrative-driven missions and explore the open world map.

Assassin's Creed Unity received mixed reviews upon release. It was praised for its visuals, customization options, setting, and characterization. Its narrative, gameplay, mission design, and multiplayer-oriented format received more divided opinions. The game was also widely panned for its numerous graphical issues and bugs, prompting Ubisoft to issue an apology and offer compensation in the form of a free expansion, Dead Kings, which acts as an epilogue to the base game's story. Players who had bought the game's season pass (which was later made unavailable for purchase in response to the controversy) additionally received a free copy of another Ubisoft title of their choice. Despite the initial critical reception, Unity was a commercial success, selling over 10 million units by May 2020. It was followed in October 2015 by Assassin's Creed Syndicate, which continues the modern-day narrative, but has its main plot set in Victorian era London.

Assassin's Creed Unity is an action-adventure, stealth game played from a third-person perspective and set in an open world environment. The game features a historical recreation of Paris in the late 18th-century at a roughly 1:1 scale. The setting is divided into seven major districts—Le Louvre, Île de la Cité, Le Marais, La Bièvre, Les Invalides, Quartier Latin, and Ventre de Paris—and also includes the town of Versailles, located on the outskirts of Paris. The commune of Saint-Denis (renamed Franciade during the French Revolution) is featured as part of the free Dead Kings expansion pack.

A number of side missions can be found and initiated from within the open world, such as "Paris Stories", which require the player to assist a non-playable character (usually a historical figure) with a minor problem; "Murder Mysteries", in which the player investigates various murder scenes, collecting clues and interrogating witnesses to determine the culprit; and "Nostradamus Enigmas", a series of cryptic riddles that lead the player to different artifacts, which can be used to unlock a special reward. Players can also find a number of collectibles scattered around Paris, including treasure chests, cockades, and artifacts, which provide various rewards, typically in the form of new gear or cosmetic options.

Unity's combat system was greatly refined over previous entries in the series, with fencing being used as an inspiration for the new system. The stealth system also saw several improvements with the addition of new features like manual crouching and the Phantom Blade, a variation of the series' signature Hidden Blade which doubles as a silent crossbow. Furthermore, the linear assassination missions from previous Assassin's Creed games were abandoned in favor of a new "Black Box" design, which offers more freedom to the player in how they go about eliminating their target; the player can explore the environment to find different entry points or possibly helpful distractions, allowing them to choose the approach that best suits them. For navigation, the game introduces new "Free-run up" and "Free-run down" commands to make it easier for the player to scale buildings in either direction, allowing them to make controlled ascents and descents at will. With the updated, larger crowds, new interactions with them are also available. The crowd regularly presents many activities, appearing organically, that the player can choose to engage in or not. Examples include scaring a group of bullies by pulling out a weapon, "settling" a fight between two civilians by killing one of them, or chasing down a thief who has just pick pocketed somebody.

For the first time in the series, the player character, Arno Dorian, presents a unique set of abilities that can be upgraded through a skill tree system, enabling the player to assign points earned through gameplay to improve Arno's skills in stealth, melee, and ranged combat, as well as his health. Players are also able to customise Arno's weapons, armor and equipment to further complement their individual style of play. The quality of these items is indicated by their level, which can be a maximum of 5 (in the case of legendary gear). Players also have a wider selection of weapons available, including swords, axes, spears, rifles, pistols and throwable items, such as smoke bombs. The Dead Kings expansion introduces an additional weapon: the Guillotine Gun - a grenade launcher with an axe head mounted under the barrel.

Like most previous Assassin's Creed titles, the game features an in-game economy system, which primarily revolves around the Café Théâtre, a former intelligence gathering front for the Assassins which has fallen into ruin and serves as Arno's main headquarters during the story. The player can renovate the Café by investing in upgrades, which change the building's interior and unlock new rooms, including a secret passage to the Assassins' underground hideout. The Café also functions as a passive business, producing revenue in the background which is deposited in a chest for Arno to collect; the more renovated the Café is, the more money it earns. Players can further increase their income by completing Café-related missions and purchasing additional taverns around Paris.