Tom Clancy's Rainbow Six Siege is an online tactical shooter video game developed by Ubisoft Montreal and published by Ubisoft. It was released worldwide for PlayStation 4, Windows, and Xbox One on December 1, 2015; the game was also released for PlayStation 5 and Xbox Series X/S exactly five years later on December 1, 2020. The title received a port for Google Stadia on June 30, 2021, and one for Amazon Luna in January 2022.[1][2] The game puts heavy emphasis on environmental destruction and cooperation between players. Each player assumes control of an attacker or a defender in different gameplay modes such as rescuing a hostage, defusing a bomb, and taking control of an objective within a room. The title has no campaign but features a series of short, offline missions called, "situations" that can be played solo. These missions have a loose narrative, focusing on recruits going through training to prepare them for future encounters with the "White Masks", a terrorist group that threatens the safety of the world. Siege is an entry in the Rainbow Six series and the successor to Tom Clancy's Rainbow 6: Patriots, a tactical shooter that had a larger focus on narrative. After Patriots was eventually cancelled due to its technical shortcomings, Ubisoft decided to reboot the franchise. The team evaluated the core of the Rainbow Six franchise and believed that letting players impersonate the top counter-terrorist operatives around the world suited the game most. To create authentic siege situations, the team consulted actual counter-terrorism units and looked at real-life examples of sieges such as the 1980 Iranian Embassy siege. Powered by AnvilNext 2.0, the game also utilizes Ubisoft's RealBlast technology to create destructible environments. The game received an overall positive reception from critics, with praise mostly directed to the game's tense multiplayer and focus on tactics. However, the game was criticized for its progression system and its lack of content. Initial sales were weak, but the game's player base increased significantly as Ubisoft adopted a "games as a service" model for the game and subsequently released several packages of free downloadable content. Several years after the game's release, some critics regarded Siege as one of the best multiplayer games in the modern market due to the improvements brought by the post-launch updates. The company partnered with ESL to make Siege an esports game. In December 2020, the game surpassed 70 million registered players across all platforms. Rainbow Six Extraction, a spin-off game featuring Siege characters, was released in January 2022.