Team Fortress 2 is a team-based first-person shooter multiplayer video game developed by Valve Corporation. It is the sequel to the 1996 mod Team Fortress for Quake and its 1999 remake.

Team Fortress 2 is focused around two opposing teams competing for a combat-based principal objective. In the game's fiction, the teams are composed of mercenaries hired by two feuding brothers to protect the company assets belonging to one brother while trying to destroy those of the other; the teams are thus represented by the names of these companies: Reliable Excavation & Demolition (RED) and Builders League United (BLU). Players can choose to play as one of nine character classes in these teams, each with his own unique strengths, weaknesses, and weapons. Although the abilities of a number of classes have changed from earlier Team Fortress incarnations, the basic elements of each class have remained, that being one primary weapon, one secondary weapon, and one melee weapon. The game was released with six official maps, although 44 extra maps, 9 arena maps, 8 king of the hill maps, and various other map types have been included in subsequent updates. In addition, a number of community assembled maps have been released. When players join a level for the first time, an introductory video shows how to complete its objectives. During matches, "The Administrator", a woman voiced by Ellen McLain, announces various game events over loudspeakers. The player limit is 16 on the Xbox 360 and PlayStation 3. On the PC, in 2008 Valve updated Team Fortress 2 to include a server variable that allows up to 32 players.

Team Fortress 2 contains many core game modes. These include Capture the Flag where the BLU and RED teams fight to steal each other's intelligence (represented in game as a briefcase) and return it to their base. At the same time, each team must defend their own intelligence. When the intelligence is dropped because of the player dying or manually dropping it, the intelligence will stay on the ground for 1 minute and return to its original location, or until picked up again by an enemy player. The intelligence can only be picked up by the opposing team. The first team to capture the intelligence three times wins. Control Points is a game mode where there are several control points laid around the map, typically 3 or 5. For a team to win they must capture all the control points within the time limit. The time limit is reset on the capture of a control point by either team. Attack/Defend consists of the BLU team attempting to capture all RED teams capture points within a time limit. RED cannot recapture a point after BLU has captured it. Another core game mode like Attack/Defend is Payload, were BLU team must typically push a cart containing a bomb through all of RED team's checkpoints within a time limit, and this time limit is extended upon BLU capturing a checkpoint. The BLU team wins by pushing the bomb cart to the last checkpoint, while RED team wins upon defending until the time limit runs out. King of the Hill is another core game mode, that contains a single control point that can be captured by both RED and BLU teams. Upon the capture of the control point, a team specific counter starts counting down and stops upon being captured by the opposing team. The first teams' timer to finish counting down wins.

There are also several alternate game modes within Team Fortress 2. Payload Race, like Payload, both RED and BLU teams push a team-colored cart to a checkpoint, unlike Payload there is only one checkpoint at the end of the track and no timer. The team to reach their checkpoint first wins. Territory Control consists of several capture points spread out across a single map. Like Control Point each point can be captured by either the RED or BLU teams. Unlike Control Point only two points are accessible at a single time, upon a team's successful capture of a point the "stage" ends and the accessible capture points change. When a team only has control of a single control point they are blocked from capturing the opposing team's control point, and the team must wait until the time limit is up and the accessible capture points change. A team wins by capturing all the control points. Special Delivery is like Capture the Flag, but there is only one briefcase that can initially be picked up by either RED or BLU team, upon a team picking up the briefcase the opposing team is now unable to pick the briefcase up until it has stayed on the ground for 45 seconds and returned to its original location. A team wins by holding the briefcase on a loading platform until they reach the top of the platform.[citation needed] Arena is a special game mode where players do not re-spawn upon death, and to win must eliminate the enemy team, or after a duration, a capture point opens, that upon capture will win the game. Mannpower is another game mode like Capture the Flag where players have access to a grappling hook and an assortment of power-ups laid around the map that gives players unique abilities.Player Destruction is a unique game mode whereupon a player's death a pickup (varies depending on the map) is dropped. To win a team must deliver a set number of pickups to the drop-off point. The player on each team with the most pickups is highlighted for everyone to see and gives passive healing to themselves and the teammates around them. PASS Time is a unique game mode inspired by rugby, developed by Valve, Bad Robot Interactive, and Escalation Studios. To win each team must score 5 goals or have the most number of goals at the end of the timer. To score a goal, a single ball, the "jack", can be picked up and thrown. Medieval is a variation on the Attack/Defend game mode where players weapons are limited to all melee weapons and other weapons that fit the medieval theme.

Mann vs Machine (MvM) is a cooperative game mode where must defend their base from waves of robots, that look like all the nine playable classes, and slow-moving tanks carting bombs. Robots and tanks drop cash upon their death, players can use this cash to buy upgrades for themselves or their weapons. The players win upon successfully defending their base from the bomb until the last wave. A paid version of this game mode called "Mann up" is also available where players buy tickets to play "Tours" with the chance to win unique cosmetics and weapon re-skins upon completion.

There also exists a Training mode and a Practice mode. Training mode exists to help new players get acquainted with basic controls, and how to play four of the nine classes. It uses wood dummies and bots to teach players. The Practice mode is just like any other multiplayer match, but only consists of the player and bots. The number of bots, their difficulty, and the map can all be adjusted to a player's preference.

Since 2009, there is typically also a Halloween-themed variation on one or more of the above modes during the weeks around the holiday, with maps or modes updated to include themed decorations and often a more difficult challenge to the players. For example, Halloween 2012 included an extremely difficult Mann vs. Machine round involving destroying more than 800 enemy forces. Due to popular demand of the Halloween events, Valve added Full Moon, the ability to play these events on the few days around the full moon throughout the year, and later Eternaween, the ability for players to vote to play the themed-events for a two-hour block at any other time